The results of the initial surveys in the cytology proficiency testing of the medical laboratories in the Province of Ontario, Canada, showed a high correlation between the opinions of the testing committee and the participants in the categories of "no abnormal cells," "metaplasia" and forms of "benign atypia." The proportion of times that slides were tested in the categories of dysplasia and malignancy in the surveys increased from 38% by the end of survey 3 to 46% by the end of survey 5. A progressive improvement in the diagnostic accuracy was demonstrated in the categories of malignancy and severe dysplasia while results were more variable in the categories of moderate and mild dysplasia. Several educational activities were initiated following survey 3, including development and circulation of demonstration sets of marked glass slides for repeated circulation to participants as well as copies of a slide/tape presentation describing the program and specific case material.