Immunological parameters including serum IgG, IgA and IgM, lymphocyte phenotypes (CD3, CD4, CD8, HLA-DR+CD3-), natural killer cell activity and lymphocyte proliferation with phytohaemagglutinin were assessed in 10 children on continuous ambulatory peritoneal dialysis (CAPD) and 10 control subjects. Live vaccines were injected into 6 of the 10 children on CAPD (4 had a combined measles-mumps-rubella vaccine and the other 2 mumps vaccine). Serum antibody titres to these viruses were measured before and after vaccination. The serum IgG level was statistically lower in the CAPD group than in the control group (P less than 0.01), but there was no difference in the percentage of HLA-DR+CD3- cells and in the ratio of CD4 to CD8 between the two groups. There were no differences in the other parameters between the two groups. All of the 6 vaccinated children seroconverted, and serious side effects were not noted. Our results suggest that children on CAPD have no significant immune impairment.