BACKGROUND: Providing doctors with new research findings or clinical guidelines is rarely sufficient to promote changes in clinical practice. An implementation strategy is required to provide clinicians with the skills and encouragement needed to alter established routines. AIM: To evaluate the effectiveness and cost-effectiveness of different training and support strategies in promoting implementation of screening and brief alcohol intervention (SBI) by general practitioners (GPs). METHOD: Subjects were 128 GPs, one per practice, from the former Northern and Yorkshire Regional Health Authority, who agreed to use the 'Drink-Less' SBI programme in an earlier dissemination trial. GPs were stratified by previous marketing conditions and randomly allocated to three intensities of training and support: controls (n = 43) received the programme with written guidelines only, trained GPs (n = 43) received the programme plus practice-based training in programme usage, trained and supported GPs (n = 42) received the programme plus practice-based training and a support telephone call every two weeks. GPs were requested to use the programme for three months. Outcome measures included proportions of GPs implementing the programme and numbers of patients screened and intervened with. RESULTS: Seventy-three (57%) GPs implemented the programme and screened 11,007 patients for risk drinking. Trained and supported GPs were significantly more likely to implement the programme (71%) than controls (44%) or trained GPs (56%); they also screened, and intervened with, significantly more patients. Costs per patient screened were: trained and supported GPs, 1.05 Pounds; trained GPs, 1.08 Pounds; and controls, 1.47 Pounds. Costs per patient intervened with were: trained and supported GPs, 5.43 Pounds; trained GPs, 6.02 Pounds; and controls, 8.19 Pounds. CONCLUSION: Practice-based training plus support telephone calls was the most effective and cost-effective strategy to encourage implementation of SBI by GPs.