To explore the relationship between providers' compliance and some key aspects of the clinical messages in practice guidelines, studies published in the English language medical literature between 1980 and 1991 were retrieved through MEDLINE and through relevant review articles in the field. All published studies providing compliance rates with practice guidelines and endorsed by official organizations were eligible for the study. The clinical content and the reported compliance rate were gathered for each recommendation in the 23 studies selected. The medical and surgical procedures addressed by 143 recommendations were identified according to specialty area, type of procedure (diagnostic, surgical, etc.) and were independently classified by the authors as being high or low on characteristics thought to influence diffusion: complexity, trialability and observability. The mean compliance rate with the 143 clinical recommendations was 54.5% (95% CI: 50.2%-58.9%), with those in the specialty areas of cardiology and oncology showing the highest compliance (mean 63.6% and 62.2%, respectively). Recommendations concerning procedures with high complexity had lower compliance rates than those low on complexity (41.9% vs. 55.9%; P =0.05), and those judged to be high on trialability had higher compliance rates than those low on trialability (55.6% vs 36.8%; P =0.03). Overall, all the characteristics of the clinical recommendations considered in the practice guidelines could account for no more than 47% of the observed variability in compliance rates. The target area of practice and the complexity and trialability of the recommended procedure appear to be useful, if partial, predictors of the level of compliance with a practice guideline.