This investigation was carried out to study possible differences in cell-mediated hypersensitivity between symptomatic and asymptomatic pigeon breeders. A variety of pigeon antigens were investigated using the indirect migration inhibition test. Cell-mediated hypersensitivity to pigeon antigens was detected in 6 of 8 symptomatic pigeon breeders, and in only 2 of 12 asymptomatic pigeon breeders. The results suggest that cellular mechanisms may be important in the pathogenesis of pigeon breeder’s disease.