Serum antibodies to avian and Aspergillus antigens were detected by enzyme-linked immunosorbent assays (ELISA) in forty-two workers from a poultry abattoir and in twenty healthy blood donors. The levels of IgG and IgA antibodies to hen and duck serum were significantly higher in poultry workers than in blood donors (P<0.01). In workers employed for less than 1 year the antibody levels were lower than in those who had been employed for a longer period of time (P<0.05). The IgA antibody level to a high molecular weight Aspergillus antigen was higher in poultry workers than blood donors (P<0-05), whereas the level of other Aspergillus antibodies were similar in the two groups. The level of IgG antibodies to hen antigen was higher in non-smokers than in smokers (P<0-02). A correlation between the antibody levels to hen and duck antigens and to pigeon antigen was found (P<0.05). indicating cross-reactivity between these antibodies. No cases of allergic alveolitis were found, and no correlation between antibody levels and respiratory symptoms could be demonstrated.