Malaria and human immunodeficiency virus (HIV) infections are common, widespread and overlapping problems in the tropics. Despite this there has been minimal evidence to support an important interaction, other than during pregnancy in multigravid HIV-infected women. The lack of an interaction in other groups is surprising, and would be unexpected based on present knowledge of anti-malarial immunity. However, most of the reported studies have been cross-sectional and performed in selected groups, making their findings difficult to interpret. Two cohort studies in children were similarly inconclusive, although both hinted at a decreased ability to control parasitaemia with more advanced HIV-disease. Recent work from Entebbe carried out in a well-characterized cohort of HIV-infected adults revealed an increase in malarial fever with deteriorating immune status. Rates by CD4+ T-cell count groups > 500, 200-499 and < 200 cells/microL were 45, 73 and 115 cases per 1000 person-years respectively, P < 0.01 for trend. These findings support an important interaction between HIV and malaria. The public health consequences and the relevance of these findings out with Entebbe are uncertain. The importance of understanding this interaction further must be a priority for sub-Saharan Africa: consequently further studies designed primarily to answer these questions will be necessary. Meanwhile, the optimism that the global malaria situation was largely unaffected by the HIV pandemic may need to be reconsidered.