A double-blind randomized trial was performed to compare the subjective morbidity of tetanus toxoid (T) with that of tetanus-diphtheria toxoid (Td). Symptoms occurred in 46 (48%) of 93 patients who received T, and in 75 of 100 patients who received Td (chi 2 = 12.3; P less than .001). The effectiveness of immunization is clear, but with shift from use of T to Td as recommended, adherence to immunization guidelines and taking of adequate immunization histories becomes even more important.