Thirty-five UK general practices in Devon and Somerset identified 2600 patients taking warfarin and sent postal questionnaires to them. A total of 1360 usable responses were received (response rate = 54.2%). One or more of the specified herbal remedies thought to interact with warfarin were taken by 8.8% of all patients. Complementary or homoeopathic treatments not specified in the survey questionnaire were taken by 14.3% of responders. Overall, 19.2% of responders were taking one or more such medicines. The use of herbal medicines had not been discussed with a conventional healthcare professional by 92.2% of patients. Of the responders 28.3% thought that herbal medicines might or definitely could interfere with other drugs prescribed by their doctor; however, patients taking any non-prescribed medication were less likely to believe this.