A quality assurance scheme for immunocytochemistry was started in 1984. There are currently 140 participating laboratories, most of which have shown considerable improvement in their results since joining the scheme. In our experience the supplier of the primary antibody does not affect the quality of the results; the sensitivity of the method used and the experience of the staff carrying out the technique are the most important factors. Participation in a scheme such as this enables laboratories to have their results compared with others and to share problems.