To explore further the mechanisms leading to immune deficiency in chronic renal failure and the role of dialysis treatment in these mechanisms. Cross-sectional and longitudinal analysis. We studied 39 children treated with peritoneal dialysis (PD), 23 children treated with hemodialysis (HD), 33 children not yet dialyzed [chronic renal failure (CRF)], and 27 healthy children. Peritoneal cells were also obtained from PD children for analysis. White blood cells (WBCs) were isolated from blood and peritoneal dialysis effluent by centrifugation. The number of CD2+, CD4+, and CD8+ T cells, B cells, and natural killer cells were measured by flow cytometry. The total peripheral blood lymphocyte count was lower in PD children (2.6 x 10(9)/L), HD children (2.1 x 10(9)/L), and CRF children (2.0 x 10(9)/L) compared with healthy children (3.1 x 10(9)/L, p < 0.05). The B lymphocyte count was also lower in PD children (0.34 x 10(9)/L), HD children (0.22 x 10(9)/L), and CRF children (0.33 x 10(9)/L) compared with healthy children (0.52 x 10(9)/L, p < 0.01). Numbers of CD4+ T cells were not different, but numbers of CD8+ T cells were lower in PD children (0.56 x 10(9)/L), HD children (0.63 x 10(9)/L), and CRF children (0.53 x 10(9)/L) compared with healthy children (0.77 x 10(9)/L, p < 0.05). The count of natural killer cells was lower in PD children (0.21 x 10(9)/L), HD children (0.17 x 10(9)/L), and CRF children (0.18 x 10(9)/L) compared with healthy children (0.50 x 10(9)/L, p < 0.0001). The CD4/CD8 ratio of lymphocytes in peritoneal effluent was 0.8 versus 1.9 in peripheral blood (p < 0.001). The CD2/CD19 ratio was not different. The cell subsets remained stable during the first year of PD treatment. The CD2/CD19 ratio in peritoneal effluent was higher in children with a peritonitis incidence > or = 1 per year. The reduced numbers of B lymphocytes, CD8+ T cells, and natural killer cells found in CRF children, dialyzed or not, may favor the frequent occurrence of infections.