The results of investigations on the distribution of planorbid snails and the prevalence of schistosomiasis mansoni by municipalities of the Espírito Santo state are presented. Nine planorbid species, belonging to three genera, were found: Biomphalaria glabrata, B. schrammi, B. straminea and B. tenagophila; Drepanotrema anatinum, D. cimex, D. depressissimum and D. lucidum; and Plesiophysa ornata. The endemic area, delimited after a preliminary survey of prevalence by homogenous microregions (1975) and another one by hydrographic basins involving 15% of the 7-14 year-old school-children population (1978-1980), comprises at least 18 municipalities along the boundary with the states of Minas Gerais and Bahia. The most frequent planorbid species was B. tenagophila, found in 44 of the 53 municipalities, followed by D. lucidum (25 municipalities), B. glabrata (23), B. scrammi (16), B. straminea (12), D. cimex (8), D. anatinum (6), D. depressissimum (5) and P. ornata (1). The presence of B. glabrata coincides with transmission of schistosomiasis. The role of B. tenagophila, which seems to be the vector in Greater Vitória, has not yet been elucidated. B. straminea only occurs in the municipalities with significant levels of endemicity, but its participation in transmission has not yet been demonstrated. The areas of highest schistosomiasis prevalence are situated in the homogeneous microregions of colatina, Colonial Serrana Espírito-Santense, Alto São Mateus and Vertente Oriental do Caparaó. Comparison between the results of the present investigation and those of previous surveys shows that, if the estimated rates correspond to the epidemiological reality, schistosomiasis prevalence has considerably increased in Espírito Santo during the last 30 years.