In adults with chronic renal failure (CRF) and/or renal replacement therapy (RRT) various immunological abnormalities have been described, but few data are available for the paediatric age group. We performed basic in vitro immunological studies in 26 patients 10 months-19 years of age with advanced renal failure, 11 with CRF (creatinine clearance 16.8 +/- 5.2 ml/min per 1.73 m2), 15 on RRT with haemodialysis (HD; n = 9) and continuous ambulatory peritoneal dialysis (CAPD; n = 6) as well as in 16 healthy controls. None had clinical evidence of deranged immune function. No significant differences were found in the percentages of B- and T-cells, T-cell subsets CD3, CD4, CD8 and mitogenic responses to phytohaemagglutinin and concanavalin A (Con A) between RRT patients (HD = CAPD) and control children. Most parameters in CRF patients were also normal, although they had a low percentage of B-cells (12.1 +/- 4.1; RRT: 19.7 +/- 6.5; controls: 18.5 +/- 7.1; P less than 0.01), relatively low levels of serum immunoglobulin G (948.4 +/- 209.4 mg/dl; HD: 1374.7 +/- 235.2 mg/dl; P less than 0.01; CAPD: 966.3 +/- 430.2 mg/dl, NS) and a high normal response to Con A (34.3 +/- 13.6 cpm x 10(-3); RRT: 24.5 +/- 11.3 cpm x 10(-3); controls: 23.4 +/- 9.9 cpm x 10(-3), P less than 0.01). All these values were, however, well within the normal accepted range. These data indicate that children/adolescents with CRF and/or RRT have no significant basic in vitro immunological defects. This study did not test the functional immune status of the young uraemic patients.