Eighteen veterinarians regularly practicing organophosphate pour-on treatment of cattle for grub infestations were examined in the course of the 1975-1976 application season for symptoms and signs as well as enzymologic and chemical evidence of organophosphate absorption. Some subjects reported headache, nausea, and irritation of the face and throat during chemical applications in poorly ventilated buildings. Organophosphate absorption was not sufficient to depress blood cholinesterase activities, and only occasionally generated measurable amounts of alkyl phosphate meatbolites in urine of exposed veterinarians.