To explore some determinants of physicians' decisions to change practice habits, we posed three questions: To what extent are some particular innovations diffused among office-based primary care physicians? What characterizes the physicians who have adopted these innovations? And, what caused them to change their behavior and adopt the innovations? Three "markers," recent innovation in medical practice, were chosen using an expert consensus technique. A telephone survey of 200 office-based pediatricians was conducted, and the physicians were asked whether or not they used the following three innovations in medical practice: continuous rather than intermittent phenobarbital for the prevention of febrile seizures, glycosylated hemoglobin measurement in the management of diabetes, and slow release theophylline in the management of asthma. The questionnaire was completed by 156 pediatricians. Of the 110 pediatricians who cared for diabetics, 73% used glycosylated hemoglobin measurement; of the 145 who saw patients with febrile seizures, 77% prescribed the continuous use of phenobarbital (if they used it at all); and, of the 152 pediatricians who cared for asthmatics, 86% reported using slow-release theophylline. The characteristics significantly associated with using the innovations were board certification, group rather than solo practice, teaching, medically related publications, academic appointment, younger age, and caring for a greater number of patients per week. For two of the innovations, discussion with a colleague was the most important source of information leading to a change of practice. The subjects cited local specialists as the colleagues who most often sparked the adoption of an innovation.