The results of longitudinal seroepidemiologic malaria surveys with the indirect haemagglutination test in four sectors in the interior of Guyana did not suggest recent malaria transmission. Indigenous malaria cases had not been detected in these sectors since 1968 but malaria surveillance here had been incomplete. The multi-stage cluster sampling method used proved to be efficient and permitted the survey of a large and sparsely populated area to be concentrated in relatively few localities. Observation of a group of 147 seropositive and seronegative persons after one year showed a four-fold or greater decline of antibody titres in five per cent of the cohort population and no such titre increases were seen, thus confirming the absence of recent malaria infections. Seropositivity rates were higher in persons with a history of malaria than in those without such a history. Collecting blood on filter paper facilitated obtaining material for serologic testing especially in the younger age group and no refusals were encountered. This advantage compensates for the slight loss in sensitivity when filter paper eluates are titrated instead of sera. The difference between the past infection probabilities of the age groups over and under 20 years old suggests that the disappearance of malaria from the interior was related more to the elimination of malaria transmission along the coast than to the specific malaria campaign in the interior.
