In a seroepidemiological study of the population of a rural area in northern Zaire, markers of hepatitis A and B were determined. Examinations of serum specimens (n = 142) showed that hepatitis A is acquired early in childhood; virtually all persons beyond 20 years of age are immune. Capillary blood dried on filter discs (n = 352) gave accurate results only in childhood; in older individuals a high percentage of positive results was missed (∼20%), presumably due to lower anti-HAV titers in older persons. The dried-blood method showed similar limitations regarding the detection of hepatitis B markers. In the 5–7 year age group there was already a high prevalence of anti-HBc (59%) as determined by the dried blood method. In the 10–19 year age group the prevalence was 94% as determined by examination of serum specimens. In all age groups the percentage of HBsAg positive persons was 20.7%, as demonstrated in capillary blood specimens and 31.7% in serum specimens.