The health situation in Sub-Saharan Africa is complex and multifactorial. Along with its poorly developed economy and lack of basic health services, vector-borne diseases and nutritional disorders are major contributors to the high morbidity and mortality seen today. Malaria and anaemia due to iron deficiency and/or to infectious diseases are rampant in the area affecting its population in general women and children in particular. Although the problem of iron deficiency and anaernia was dealt with varying strategies in different places iron supplementation is widely used in many developing countries and has become a routine procedure in maternal and child health programmes. In recent years, however, there has been a growing concern regarding this approach due to the emergence of conflicting evidence on the health outcome of iron supplementation. In addition to the beneficial effect of iron supplementation, a possible adverse effect on health, particularly on the risk to malaria, has been suggested. The continued controversy has raised doubts as to whether to implement iron supplementation programmes in malaria endemic areas. A randomised, placebo-controlled field trial was conducted in a malaria endemic area in the northwestern part of Ethiopia in May 1993-October 1995 to determine the haernatological response to oral iron supplementation and measure the risk of malarial illness associated with iron. The study involved 776 women and 841 children with low haemoglobin (HB) level who were randomly allocated to receive oral iron or a look alike placebo for a period of 12 weeks. The results of this study showed that anaernia is common in the study population with prevalences of 72.3% and 84.6% among women and children respectively. The content of the staple diet in the area was generally iron insufficient. The dietary iron insufficiency was further realised to be both due to inadequate intake and poor absorption of the iron ingested. The supplementation for 12 weeks was completed by 729 (93.9%) women and 740 (88%) children in the study. After supplementation more women (82.6%) and children (93.5%) in the iron group showed an improvement in their FIB compared with those women (54.6%) and children (43.7%) in the placebo respectively. The mean HB rise was also significantly higher in women and children in the iron than in the placebo group, 1.43 vs 0.28 g/dL, (t= 12.6; p<0.0001) for women and 1.38 vs 0.22 g/dL Q=21.3; p<0.0001) for children respectively. After supplementation women and children with severe anaemia were fewer in the iron (5.1% and 0.3%; x 17.2; p<0.001) than in the placebo group (13.5% and 8.0%; y, 2 =27.9; p<0.001) . After supplementation more women (9.6%) and children (18.2%) in the iron group reached the HB cut-off point showing no anaernia than women (1.4%) and children (9.6%) who received placebo (X2" =23.9; p<0.001 and X2 =34.3; p<0.001 for women and children respectively). Post-supplementation prevalences of clinical malaria among women in the iron and placebo groups were 24.2% and 18.3% respectively (RR=1.3, C1,1.0-1.8). The parasite rate was also higher in the iron supplemented women than those in the placebo, 29.4% and 20.2% respectively (RR=1.47, Cl, 1.4-1.9). During supplementation, women in the iron group experienced more frequent episodes of fever and spent more days with fever than women in the placebo group, (RR=1.16, CI, 1.03-1.30). Similarly, clinical malaria was diagnosed in 19.7% and 13.2% of children in the iron and placebo treatment groups respectively, (RR=1.49, CI, 1.07-2.08). Splenomegaly in children was detected in 27.3% of those in the iron 19.1% of those in the placebo, (RR=1.43, Cl, 1.1-1.9). The parasite rates for iron and placebo supplemented children were 34.5% and 27.1% respectively, (RR=1.28, Cly 1.0-1.6). Febrile episodes were experienced by 68.9% and 58.9% of children in the iron and placebo groups respectively, (RR=1.17; CI, 1.05-1.30. The results indicated not only that the dietary iron intake of the population was inadequate but also was poorly bioavailable due to lack of foods which enhance absorption and due to a high intake of food substances which interfere absorption all of which may have contributed to the anaernia. Study women and children who received iron supplementation have shown a substantial haernatological response (HB rise) and significantly improved their anaemia. The study has also demonstrated that there is a considerable risk of uncomplicated malaria associated with oral iron supplementation as malariometric indices used in this study were all significantly higher among women and children in the iron than in the placebo group. Intervention programmes involving iron supplementation in malaria endemic areas in the future need to weigh the health benefits and the malarial risk attributable to iron. In the present study area,w here nearly all women and children suffer from anaerniaa nd its consequenceso n health, the haematological response to iron supplementation outweighs the associated drawbacks. In such areas oral iron supplementation should therefore continue to be used to prevent and control iron deficiency and anaemia. Public health activities pertaining to the control and prevention of malaria and/or anaernia should, however, protect the population most at risk from malaria when implementing iron supplementation during the malaria transmission seasons.