Women eligible for the Canadian randomized trial of chorionic villi sampling (CVS) often cite physician influence as a reason for refusing to participate. To measure directly physicians' attitudes to and knowledge of prenatal diagnosis (PND), amniocentesis, CVS, randomized trials, and the Canadian trial, a 3-page questionnaire was mailed to all registered obstetricians in British Columbia (BC) and in Montreal (Mtl). The overall response rate was 70%. Most physicians thought PND was important and that it was their role to discuss and advise PND to their patients. Physicians were split in their preferences for amniocentesis or CVS (32% vs. 34%); reasons for their preferences paralleled those given by women studied previously by us. Physicians who thought CVS was too experimental, who were hesitant about the trial or who were less likely to discuss the study with patients were older, less likely to have participated in a randomized trial previously and less comfortable with randomization and discussing uncertain risks with patients. Mtl physicians were less aware and more hesitant about the Canadian trial than those in BC. Moreover, Mtl physicians were more likely to consider the ongoing trial inappropriate and too experimental than BC physicians. Because physicians act as "gatekeepers," educating them about new technologies and about randomized studies is essential for ensuring both participant's access to a new procedure and success of the randomized trial.