The chemical control of sheep ectoparasites raises important environmental, health and welfare issues. There is increasing concern about the possible harmful effects of pesticides on human health and the role of dipping in the contamination of natural watercourses. A longitudinal survey was conducted in 1991, the last year of compulsory dipping for the control of sheep scab, to obtain information about the chemical control of ectoparasites on 485 farms in England and Wales. Organophosphate insecticides were the most commonly used for both summer and compulsory dipping and for spraying sheep, although many of the products used for spraying sheep were not licensed for this purpose. The early pattern of dipping and spraying appeared to follow the pattern of incidence of blowfly strike although more than 40 per cent of sheep were dipped during the first two weeks of the compulsory dipping period. Compulsory dipping for the control of sheep scab was reduced from two dips to one dip between 1988 and 1989 and removed altogether in 1992. The results from the survey were compared with the results of a previous survey and showed an apparent decline in the use of dipping and an increase in the use of alternative methods of control between 1988 and 1991.