In this study, CD4(+) and CD8(+) T cells and antibody levels were measured in 94 migrant fishermen infected with Schistosoma japonicum from Dongting Lake, China. Prevalence among these fishermen was high (63.8%), with a mean infection intensity of 61.4 +/- 3.8 epg, and included a high proportion of individuals (39.4%) with substantial parenchymal fibrosis (stages > or = 2/3). The CD4(+)/CD8(+) ratio in men (1.34 +/- 0.11) was significantly lower than that of women (1.58 +/- 0.15). CD4(+) T cells and the ratio of CD4(+)/CD8(+) were significantly decreased both in subjects infected with S. japonicum and those with parenchymal fibrosis. However, levels of total IgA, IgM, and anti-schistosome egg antigen IgG correlated positively with infection intensity and pathologic lesion number. These results suggest an imbalance between cell-mediated and humoral immunity in these fishermen, the precise cause of which remains undetermined.