In recent years, it has been recommended that “high-risk” patients receive influenza immunizations annually. During the 1976 National Influenza Immunization Program, a higher priority was given to these patients than to the general population. The present study was undertaken to compare the antibody response of high-risk patients with that of a group of individuals with no underlying disease after immunization with 0.5 ml of bivalent, split-virus vaccine containing 200 CCA units each of influenza A/New Jersey/76 and A/Victoria/75. Sera were obtained before and after immunization from 41 “healthy” volunteers and from 57 cardiology, 31 hematology, 13 hemodialysis, and 16 renal transplant patients. The control, cardiology, and hemodialysis groups responded equally well to A/Victoria/75 antigen, but the hematology and renal transplant groups did not respond as well (P < .05). Only the hematology patients responded at a significantly lower level (P < .05) than the control group to A/New Jersey/76. The control and renal transplant groups had a significantly greater response to A/New Jersey/76 antigen than to A/Victoria/75 antigen (P < .002). Although the same pattern was demonstrated by the other patient groups, the differences were not significant. Because hematology and renal transplant patients responded relatively poorly to influenza immunization, prophylactic administration of amantadine during influenza outbreaks should be considered in patients with renal function adequate to excrete this drug.