Background: Haemophilus influenzae infection is a mild and self-limited disease in the healthy population. However, it may show an aggressive course in the immunocompromised state which underlines the importance of vaccination against this agent. On the other hand, posttranplant immunosuppression may impair immune responses and thus the efficacy of the vaccination. Methods: Forty-three renal transplant recipients with well-functioning allografts were immunized with H. influenzae type b vaccine in order to investigate the immune response. The patients received a double or a triple immunosuppressive protocol. Seven healthy members of the dialysis unit served as controls. After obtaining basal serum samples, the patients and the control subjects were immunized with H. influenzae type b conjugate vaccine. After 6 and 12 weeks, serum samples obtained again to determine H. influenzae type b antibody titers. Results: The antibody titers 6 and 12 weeks after vaccination were significantly higher as compared with the basal values, similar to those of the control subjects. These titers did not show statistically significant differences between the double and triple immunosuppressive therapy groups. After 12 weeks of vaccination, the antibody titers did not show a statistically significant difference as compared with those obtained after 6 weeks. Conclusion: H. influenzae type b vaccination is safe and effective in patients with well-functioning renal allografts and should be recommended to renal transplant recipients who may have the risk of invasive disease on the basis of the immunosuppressive state.