Clinical features in 173 white expatriates returning to Britain with the sole diagnosis of schistosomiasis were compared with those in non-infected control subjects, matched for age and sex, returning from similar endemic areas. Infection was, with one exception, acquired in Africa. Schistosoma mansoni was found in 135 patients, S haematobium in 29, and mixed infection in 9. 79% of patients with S haematobium had symptoms, compared with 47% of patients with S mansoni. Tiredness, headache, and gastrointestinal disturbance were no more frequent in symptomatic patients than in control subjects. In over 50% of patients with schistosomiasis the diagnosis was established from snips of rectal mucosa, and this raises the question of how best to look for infection in those who have been exposed. Urine examination and schistosomal serology appear to be the best screening methods; patients with haematuria or seropositivity should be investigated further.