Veterinarians representing one third of the Norwegian fish farms were asked about the clinical use of dichlorvos and trichlorfon by use of a questionnaire. A total of 45 veterinarians had experience in treatment of salmon lice with these organophosphates. Fourty-nine percent of the veterinarians reported that the fish farmers in their region solely used the recommended treatment equipment when delousing the fish, of these 1/4 always oxygenated the treatment solution. Repeated treatment were always prescribed by 24% of the veterinarians, while 44% did this occasionally. Of the 45 veterinarians 7% were often present and 44% were occasionally present at the fish farms in connection with the treatment. The answers showed that compliance with the recommended treatment procedures was unsatisfactory.