The circadian variation of Scht Dukes and Davidson, 1968; Doehring et ai., 1983) and a general recommendation to do parasitological testing for urinary schistosomiasis at noon, was made. Since hematuria and proteinuria result from microlesions due to the eggs passing through the bladder wall (Wilkins et al., 1979; Doehring et al., 1985), their levels were also expected to fluctuate during the day. In fact, Weber et al. (1967) found in one patient in Zimbabwe that visible hematuria occurred only in the afternoon, and Doehring et al. (1985) described a circadian cycle of proteinuria (with a peak at 12:00 h) and of hematuria (with a peak at 18:00 h), in five infected boys in the Sudan. Reagent sticks detecting hematuria and proteinuria are a valuable alternative for the diagnosis of S. haematobium infections (Mott et al., 1985) and they have been recommended for large-scale use in morbidity control programmes (Wilkins et al., 1979; Savioli and Mott, 1989). But to our knowledge, no recommendation about the optimal reagent stick testing time has yet been made. We therefore investigated whether the circadian variation of hematuria and proteinuria had an influence on the diagnostic performance of reagent sticks. This study was carried out in Idete primary school (Kilombero District, Southeastern Tanzania). The content and aims of the study were discussed with the teachers, who explained them comprehensively to the children. Parents were fully informed on their request. Two days before testing, all children of class 3-6 (n = 144) were screened at 14:00 h