A group of 31 school children from Gabon infected with Schistosoma haematobium was examined before praziquantel therapy and followed on days 3, 9, 14, 21, 24, 28, 31 and 35 after therapy. The day-to-day variation of schistosome circulating antigens, urinary egg output, and the reagent strip index (RSI, a pathologic marker) was studied in six consecutive pretreatment urine samples collected under standardized conditions. The geometric mean pretreatment for egg output ranged between 97 and 223 eggs per 10 ml of urine; for urine circulating anodic antigen (CAA) levels this was 44-154 pg/ml and for circulating cathodic antigen (CCA) levels this was 180-601 pg/ml. On the day of treatment, 97% of the children had viable eggs in their urine, 87% had a positive RSI; positive CAA levels were detected in 61% of the children and positive CCA levels in 77%. A significant correlation was consistently found between RSI and egg counts. Five weeks after chemotherapy egg output, levels of CAA and CCA and the severity of pathologic findings in the lower renal tract, as indicated by the RSI, had decreased significantly in all cases. Our results indicate that egg output in urine is an accurate method for diagnosis of S. haematobium, and additionally show less day-to-day variation than detection by ELISA of schistosome circulating antigens in urine.