Health professionals are reluctant to enquire actively about cancer patients' concerns and feelings. They fear that probing will damage patients psychologically and believe they have had insufficient training in the relevant interviewing skills. In considering how their interviewing skills might be improved, the key question is which interviewing behaviours promote patient disclosure and which inhibit it. To test our predictions about the utility of specific interviewing behaviours, we asked 206 health professionals, who were attending workshops on communication and counselling skills, to interview a simulated patient before and after the workshop to establish the patient's current problems. They were given 20 min to do this and the interviews were tape-recorded and transcribed to permit detailed assessment by trained raters using an utterance by utterance analysis. This permitted the form, function, content and emotional level of each utterance to be rated. Correlation coefficients were calculated between specific interviewing behaviours and patient disclosure of significant information. Significant information was defined as any information disclosed by patients about their perceptions of their illness or prognosis or any adverse physical, psychological or social sequelae of their cancer and treatment. Spearman correlation coefficients were calculated between specific interviewing behaviours and patient disclosure. The use of these behaviours by those 41 (20%) of interviewers who achieved most disclosure was compared with those 41 (20%) who obtained least disclosure. Patient disclosure of significant information was promoted by the use of open directive questions, focusing on and clarifying psychological aspects, empathic statements, summarising and making educated guesses. The use of leading questions, focusing on and clarifying physical aspects, moving into advice and reassurance mode inhibited patient disclosure. Inhibitory behaviours were used 2-3 times more frequently before training than facilitative ones. Training of health professionals involved in cancer care should, therefore, ensure they acquire these positive skills and relinquish the inhibitory behaviours.