Estimations of the incidence of hepatocellular carcinoma (HCC) for the period 1968-74 in the Province of Inhambane, Mozambique, have been calculated and together with rates observed in South Africa among mineworkers from the same Province indicate very high levels of incidence in certain districts of Inhambane. Exceptionally high incidence levels in adolescents and young adults are not sustained at older ages and suggest the existence of a subgroup of highly susceptible individuals. A sharp decline in incidence occurred during the period of study. Concurrently with the studies of incidence, 2183 samples of prepared food were randomly collected from 6 districts of Inhambane as well as from Manhica-Magude, a region of lower HCC incidence to the south. A further 623 samples were taken during 1976-77 in Transkei, much further south, where an even lower incidence had been recorded. The mean aflatoxin dietary intake values for the regions studied were significantly related to HCC rates. Furthermore, data on aflatoxin B1 contamination of prepared food from 5 different countries showed overall a highly significant relationship with crude HCC rates. In view of the evidence that chronic hepatitis B virus (HBV) infection may be a prerequisite for the development of virtually all cases of HCC and given the merely moderate prevalence of carrier status that has been observed in some high incidence regions, it is likely that an interaction between HBV and aflatoxin is responsible for the exceptionally high rates evident in parts of Africa and Asia. Various indications from Mozambique suggest that aflatoxin may have a late stage effect on the development of HCC. This points to avenues for intervention that could be more rapidly implemented than with vaccination alone.