Abstract AIM: To determine the impact and cost-effectiveness of telephone versus written access to magnetic resonance imaging (MRI), and of different strategies for disseminating locally produced guidelines, upon requests by general practitioners (GPs) for knee and lumbar spine investigation. MATERIAL AND METHODS: Two sequential pragmatic open cluster-randomized trials were conducted within 39 general practices. The outcome measure in each trial was concordance of request with local guidelines. Trial 1: practices requested MRI by telephone or in writing. Trial 2: all practices received guidelines, plus either: a practice-based seminar, practice-specific audit feedback, both seminar and feedback, or neither. RESULTS: A total of 414 requests were assessed in the two trials. Trial 1: telephone access cost £4.86 more per request but rates of concordant requests were equivalent (65%/64%: telephone/written). Trial 2: compared to the control group, costs per practice were £1911 higher in seminar group, £1543 higher in feedback group and £3578 higher for those receiving both. Concordance was greater following the intervention (74% vs 65%; P < 0.05), but there was no difference between the four study groups. CONCLUSIONS: Method of access did not affect concordance. Written access was more cost-effective. Seminars and feedback were no more effective in modifying practice than guidelines alone, which was thus the most cost-effective option. Robling, M.R. et al. (2002). Clinical Radiology 57, 402–407.