Studies evaluating relationships between physician background characteristics (e.g. years of practice and medical training) and quality of care have found few consistent associations. Site of practice variables have been better predictors of quality than have characteristics of individual physicians. This study explores the relationship between physicians' knowledge and attitudes regarding the use of blood products, and the quality of their transfusion practice, based on in-depth physician interviews and medical record reviews. The sample includes 296 transfusion episodes ordered by 17 physicians in 2 teaching hospitals. The physicians had participated in a larger survey of staff surgeons and anesthesiologists in these hospitals. The quality of transfusion practice was defined as the proportion of a physicians' transfusion episodes scored as justified, as determined by explicit chart audit plus implicit physician review. Large baseline differences were observed between the 2 hospitals; 48% of transfusions in hospital A were justified compared with 81% in hospital B. At the physician level, knowledge of transfusion indications and receptivity to input from colleagues were significantly associated with higher quality transfusion practice (standardized betas = 0.41 (P = 0.01), and 0.40 (P = 0.02), respectively). These findings suggest that in addition to organizational context, physician characteristics may be associated with the quality of care related to a specific clinical practice.