Current strategies for schistosomiasis control rely heavily on drug treatment intended to reduce morbidity and disease to an insignificant level of public health importance. This approach reduces but rarely, if ever, eliminates transmission. Indeed, snail infection rates may be little altered by such chemotherapy. Reinfection is inevitable. The mean human community prevalence usually returns rapidly to precontrol levels but the mean intensity of infection takes much longer, distorting the general relationship between the two. Because of the focality of schistosomiasis transmission, retreatment based on mean population prevalence is often too late to protect people living near active transmission sites. However, if suitable methods can be developed to examine man after treatment, they should simplify the detection of the main transmission sites, allowing the employment of alternative, focal control measures to consolidate the beneficial effects of mass chemotherapy.