We monitored the responses of solid organ transplant recipients (SOTs) to influenza vaccine during consecutive influenza seasons. Standard 1993-1994 trivalent influenza vaccine was given to 68 SOTs and 29 healthy young adults, and hemagglutination-inhibition (HI) antibody titers were determined pre- and post-immunization. Significant rises in geometric mean antibody titers occurred post-immunization for all three antigens in both groups. However, the magnitude of the rise was lower in SOTs (1.5-2.3-fold vs. 8.7-10.4-fold, depending on the antigen) (P < .05), and significantly fewer SOTs bad protective HI titers (≥1:40) for B/Panama/45/90 antigens (50% of SOTs vs. 76% of healthy subjects) and for A/Texas/36/91 (H1N1) antigens (60% vs. 90%). After exclusion of persons with high preimmunization titers, SOTs had significantly reduced frequencies of ≥4-fold antibody responses compared with those of healthy subjects (23%-38% vs. 86%-100%) (P < .05 for each antigen). When a series of two injections of standard 1994-1995 vaccine was given to 23 SOTs, there was no significant improvement in vaccine response with the second dose. Some SOTs have deficient responses to inactivated influenza vaccines.