All eight production workers from a small trout-processing factory were studied because of respiratory or rhinitis symptoms when working next to the automatic gutting machine. Seven of the eight had positive histamine provocation tests. Four patients had elevated total IgE levels while one had a slightly elevated eosinophil count. All workers had either weakly or moderately positive RAST against contaminated water from the outlet drain of the gutting machine. This water contained 1 microgram endotoxin/ml. We concluded that five of the workers had probably developed occupationally related asthma from inhalation of contaminated aerosol from the gutting machine. Inhalation of endotoxin from gram-negative bacteria may be the cause of this disorder. An alternative explanation is a Type I allergy caused by fish or bacterial protein with or without a simultaneous effect of endotoxin.