From 1977 to 1982, the authors attempted a malaria suppression trial in North Mare District, Tanzania, to see whether the incidence of Burkltt's lymphoma (BL) could be lowered by reducing the level of malarial infection in a child population below 10 years of age. immediately after initiation of the suppression trial, the prevalence of malaria fell drastically in the Mars children; however, soon after, the rate of malarial infection rose again in the trial area in spite of continued chloroquine distribution, and by 1981 the prevalence of malarial infection again reached the high levels that had prevailed in the North Mars lowlands before 1977. However, during the period of chioroquine distribution in North Mare, the level of malarial infection there was constantly lower than that observed in a comparison area in South Mars, although the two areas had been similar with respect to malaria endemicity prior to the intervention. During the years of chloroqulne distribution in North Mars, the incidence rate of BL there fell consid erably, from about 4 per 100, 000 population to about 1 per 100, 000 population, and it rose again to pretrial levels in 1984, that is, about two years after the chioroqulne distribution had been termInated. This apparent association between malaria suppression and decline in BL incidence at first seemed to indicate that malaria is a causal factor in BL production. A closer scrutiny of the survey data revealed, however, that the decline in BL incidence might have started several years before the chioroquine distribution began; thus it appears that the malaria suppression could not have been the sole cause of the BL decline.