Field studies on the morbidity of schistosomiasis mansoni were carried out in some rural endemic areas of Northeastern Brazil during the first semester of 1991. These cross-sectional studies were limited to the assessment of the gradient of clinical forms of the disease. The entire population present in a house-to-house survey was examined. Results have shown a reduction in the prevalence rates of the more severe form of schistosomiasis, the hepatosplenic form, when compared with previous similar studies made in the same areas during the 1960s and 1970s. Changes in prevalence rates of the severe clinical forms from the younger to the older age groups were observed.