A significant reduction in the prevalence of both intestinal and urinary schistosomiasis has occurred in all emirates (districts) in all 12 foci of the infection distributed in five regions of Saudi Arabia. Infection with Schistosoma mansoni has dropped in foci of the infection in the Central Region (Riyadh and Hail) and in all foci within the western provinces. Reduction has also occurred in the prevalence of S. haematobium in foci of Gizan, the Red Sea coastal areas and parts of Madinah. The disease no longer exists around Riyadh. The overall prevalence in all 12 foci of infection in Saudi Arabia dropped gradually from 11% in 1983 to 1.9% in 1987. At present the infection rates among expatriates are much higher than among Saudis in most foci. The number of emirates which had rates of 10% or more has dropped from 46 in 1983, to nil in 1987, and the number with rates of 5-10% from 25 in 1983 to one in 1987. The overall prevalence is presently between 1 and less than 5% in 73 emirates and less than 1% in 41 emirates. Significant reduction was observed in most villages in each district. Higher infection rates may still be present in a few areas within one or two emirates not surveyed in the last 2-3 years. The potential danger of a resurgence of the disease due to the development of water resources and the presence of a great number of infected expatriates is significant.