450 patients in Riyadh, Saudi Arabia, complaining of chronic abdominal pain and, coming from different countries endemic for schistosomiasis, were examined endoscopically using fibre-optic colono- or sigmoidoscopes, and rectal biopsies were examined for Schistosoma mansoni ova. After a preliminary study showed that more than 6 biopsies did not increase the positivity rate, 6 biopsies were taken from the rectum and examined by the transparency technique. 280 were positive for S. mansoni, 9 of them having in addition S. haematobium. 4 patients had polyps in the sigmoid colon and rectum. When these positive cases were examined using duplicate 50 mg Kato smears, only 160 (57.1%) were positive. There was a highly positive correlation between the intensity of infection as graded by the 2 techniques. We recommend examination of 6 rectal biopsies using fibre-optic sigmoidoscopy when available in small communities with a patchy distribution of schistosomiasis like Saudi Arabia. The method could also be used to exclude schistosomiasis in persons who have moved from rural to urban or non-endemic areas and are unlikely to be re-exposed to infection.