To evaluate response-aiding strategies feasible in large surveys, we randomly allocated general practitioners (GPs) to one of four intervention groups: Group 1 received 'exhaustive' telephone prompts by a medical peer in advance of a questionnaire; Group 2, inclusion of an embossed pen with the questionnaire; Group 3, an advance letter prompt; and Group 4, a 'single attempt' advance telephone prompt by a non-medical research assistant. Follow-up procedures were identical. Response rates by group were not significantly different overall (chi 2 = 4.59, df = 3, p = 0.20) although advance prompts by a medical peer were significantly more effective than other strategies for male GPs. The difference in overall response rates between males (63%) and females (74%) was significant (chi 2 = 15.40, df = 1, p < 0.01). No other response bias was evident. Our demonstration of a significant interaction between respondent sex and response-aiding strategy invites further research.