In a fishing community on Lake Albert in Uganda the pattern of intensity of Schistosoma mansoni infection 6 months after treatment with praziquantel was found to be very similar to reinfection patterns seen in previously studied endemic communities: the profile peaks sharply at around the age of 10 years falling away rapidly to much lower levels in adults. This is in stark contrast to the patterns of water contact, which differ greatly between fishing and non-fishing communities. On Lake Albert, adults appear to be more heavily exposed than children. From these observations we conclude that adults are physiologically (perhaps immunologically) more resistant to infection after treatment than children.