This thesis describes the application of new malariological techniques to study some of the problems facing, or which might face, the malaria control programme in The Gezira (Blue Nile Province) of The Sudan. Serological tests, using the indirect fluorescent antibody test were carried out on a large sample of the population of the Gezira in 1977 and 1979 drawn from 18 localities in 4 different areas. The results showed a much higher level of prevalence and incidence of malaria than was detected by routine parasitological examinations. The percentage of those who had positive antibody reactions decreased in 1979 from that of 1977 in North, West, and South Gezira, but in Central Gezira there was a significant rise from 27% to 75%, indicating the presence of a high level of transmission. This coincided with malathion resistance of the vector in this area. Eggs from females of Anopheles arabiensis, the main malaria vector there, which had survived field tests on malathion were brought to London and reared for further testing and genetic studies. A population which survived exposure to 5% malathion for S hours was selected. Crossing and backcrossing of this population with three different malathion-susceptible populations of A. arabiensis showed an involvement of one gene in the resistance, which appeared to be of dominant nature. Tests with Fenitrothion, Fenthion, and Propoxur gave total kills, showing no signs of cross-resistance. There was no indication of resistance to Malathion or to Temephos (Abate) at the larval stages. The spread of drug resistant human malaria parasites is a possible danger for the future of malaria control in Africa. A micro in vitro test for drug resistance was developed using rodent and primate malaria parasites as model5, as well as blood from human malaria cases in London. Radioactive chloroquine was used in a social study to estimate the adsorption of low concentrations of the drug to plastic and glass vials which might affect the results of the micro test. Approximately 20% loss was observed. A limited field trial of the micro-test in the Sennar Area (Blue Nile Province) showed no clear indication of drug resistance at the present time. These results confirmed those of in vivo tests done at the same time.