Following the report of ten cases of respiratory illness in processors of frozen king crab, we investigated the conditions of work and the pulmonary and immunologic status of the workers in three crab-processing and one fish-packing (control) plant. Pulmonary function was measured before and after work, and skin tests were performed in subgroups matched for age, sex, and duration of current employment. The antibody response to king crab antigens was examined in sera from the subgroups and another (unrelated) control group. Extracts of crab meat, shell, and processing dust were used for skin testing and precipitin detection. FEV1, FVC, and MEFR decreased during the day in two crab processors, and precipitins were evident in sera from nine, but findings were normal in the fish packers. Crab meat elicited the strongest response, with multiple precipitin bands in some cases. Control sera showed no reaction. There was correlation between serology, results of skin tests, and symptoms. It is concluded that the inhalation of aerosolized crab antigen(s) may cause respiratory symptoms and can cause immunologic effects similar to those caused by other occupational respiratory allergens. We recommend preplacement and periodic medical examination of workers in crab-processing plants, improved ventilation in processing areas, and programs to discourage smoking.