1. The attitudes and knowledge of doctors in the Northern Region to reporting of adverse drug reactions were assessed using a postal questionnaire to all doctors in two, previously identified, high reporting and two low reporting health districts. Comparisons were made of the attitudes and knowledge within professional groups (GPs, Consultants and Junior Hospital Doctors), and between the amalgamated doctor groups. 2. 1181 of 1600 doctors (74%) responded. Despite being selected on the basis of previous adverse drug reaction reporting patterns, GPs and consultants from high and low reporting districts perceived they had sent a similar number of ADR reports, and there were few differences in opinion and attitude within these two groups. 3. Most differences within doctor groups were found for junior doctors, with those from low reporting districts indicating they had sent significantly less yellow cards than those in high reporting districts. There were also significant differences in the estimates junior doctors made with a frequency of adverse drug reactions, the existing documentation on adverse drug reactions, and the purposes of the adverse reaction scheme. 4. General Practitioners in low reporting areas stated they wrote more prescriptions (P < 0.02), consultants spent more time in clinical contact (P < 0.01) and junior doctors did both (P < 0.01), all of which suggest different workloads may effect reporting of adverse drug reactions. 5. When given clinical examples, or asked about the CSMs black triangle scheme, all doctor groups performed poorly. 6. The number of reports stated as being sent increased with time from qualification for 10 years, then seemed to plateau.(ABSTRACT TRUNCATED AT 250 WORDS)