A random sample of Maryland physicians stratified by practice specialty (family, general, internal medicine, cardiology, and nephrology) was surveyed before and one year after dissemination of the 1984 Report of the Third Joint National Committee on the Detection, Evaluation, and Treatment of High Blood Pressure (The JNC III Report). Fourty-four per cent of the total eligible sample responded to both questionnaires. One year after publication, 62 per cent of physicians participating in both parts of the study were aware of the report. Although availability of a copy (58 per cent), familiarity with the recommendations (81 per cent), and the extent to which care was based on the guidelines (65 per cent) were high, use of the report in practice (17 per cent) and the amount of change in practice behavior required to adhere to the guidelines (18 per cent) were low. Prior to publication of the report, more than two-thirds of responding physicians were found to be practicing in a manner congruent with nine of ten treatment recommendations studied. One year after JNC III's release, they reported practice behavior which was not significantly different. It seems that this consensus report codified, rather than changed, practice behavior in this sample.