Anti-influenza antibody (Ab) titers were measured in order to elucidate whether there are any disturbances in Ab production in chronic renal failure (CRF) patients. A total of 55 CRF patients plus 15 normal individuals were vaccinated with influenza vaccine twice, 4 weeks apart of the 55 CRF patients, 15 were not on dialysis, 10 were undergoing hemodialysis (HD), and 30 were on continuous ambulatory peritoneal dialysis (CAPD). Of the 30 CAPD patients, 14 had peritonitis. Serum Ab titers were measured by complement fixation (CF) and hemagglutination inhibition (HI) tests, and IgG and IgM class specific antibodies by ELISA. All groups responded to immunization, but CAPD patients with peritonitis and CRF patients not yet on dialysis did not show a significant elevation in IgM class Ab titers. The number of CAPD patients with peritonitis who achieved positive titers was significantly lower in HI (p less than 0.01) and IgG class antibodies (p less than 0.05) compared with normal controls. Two patients with frequent peritonitis did not show any response to vaccination. It was concluded that patients with renal dysfunction have some abnormalities in Ab production against influenza vaccine, the effects of which were more pronounced in the CAPD patients with frequent peritonitis.