Twenty Schistosoma mansoni strains were isolated from three groups of patients (intestinal, hepatointestinal and hepatosplenic clinical forms) born and living in the town of Capitão Andrade, Minas Gerais, Brazil. Schistosomal isolate from each group was inoculated into three sets of mice with 25, 50 and 100 cercariae. The animals were killed 90 and 180 days after infection and submitted to extensive histopathological study of the liver, lung, intestine and spleen to determine qualitative and quantitative morphological characteristics, mainly of the granulomas. The histopathological changes caused the same patterns of infection in mice and were proportional to the inoculum and the time of infection, confirming the relevance of quantitative aspects in the determination of the disease. These data indicate three possibilities: (1) mouse model is not adequate to predict possible differences in the S. mansoni isolates obtained from patients; (2) field isolates are probably genetic polymorphic and undifferentiated; (3) schistosomiasis in human does not depend on parasite intrinsic factors, but on multivariable factors, such as intensity and duration of infection, time of infection, age and gender and other characteristics such as host response.