Infection with Schistosoma mansoni induces a wide range of effects on the immune responses of the host. In the present study we investigated the influence of soluble egg antigens (SEA) on the cell cycle of peripheral blood mononuclear cells (PBMC) from infected and non-infected individuals with S. mansoni resident in an endemic area and blood donors from non-endemic area. The cell cycle, the expression of activation markers and cyclin D(+)(1,2,3) CD3(+) frequency was assessed by flow cytometry. Stimulation of PBMC from infected patients with SEA resulted in a lower frequency of CD3(+) T cells in S phase when compared with the non-infected group. In addition, infected patients presented a decrease of activation marker expression (CD69(+), HLA-DR(+) and CD28(-) on CD4(+) cells and CD25(+), HLA-DR(+) on CD8(+) cells). A reduced frequency was observed of cyclin D(1,2,3) expression in SEA-stimulated T cells from infected individuals when compared with those from the non-infected group. The decreased expression of activation markers and frequency of cyclin D(1,2,3) in T cells may result in arrest of T cells in the G(0)/G(1) phase of the cell cycle, thus explaining the down-regulation observed in chronic schistosomiasis.