Metabolic acidosis negatively influences dietary intake, increases protein catabolism, and deteriorates nutritional status. In the present study, we evaluated in peritoneal dialysis (PD) patients whether parameters of blood acid-base equilibrium influence total and subpopulation lymphocyte counts (TLC, SLCs), which are markers of the immunologic and nutritional status of dialyzed patients. Studies were carried out in 55 patients, mean age 50.9 +/- 12.4 years, treated with PD for a mean of 22.2 +/- 11.4 months. Parameters of blood acid-base equilibrium were measured simultaneously with evaluation of TLC and SLCs. (Antigens CD3, CD4, CD5, CD8, CD19, CD16+56 were determined using flow cytometry.) The study patients showed compensated metabolic acidosis (pH: 7.40 +/- 0.04; HCO3-: 22.9 +/- 2.4 mmol/L). Statistical analysis revealed significant (p < 0.05) positive correlations of bicarbonate blood concentration and base excess with TLC and with CD3, CD5, and CD8 cell counts, but not with CD19 and CD16+56 cell counts. The CD4 cell count correlated only with blood bicarbonate level. Patients on PD who show better correction of metabolic acidosis also show higher TLC and CD3, CD4, CD5, and CD8 cell counts. The numbers of B lymphocytes (CD19) and natural killer cells (CD16+56) are not directly related to bicarbonate blood concentration, at least in the examined range.