The STOP Project is a randomized clinical trial designed to evaluate the effectiveness of a behavioral intervention program to encourage cessation of smoking by pregnant women attending routine prenatal care in private physician settings. This project is a collaborative effort between the NICHD and the American College of Obstetricians and Gynecologists. The unit of randomization in STOP will be a practicing physician's population of pregnant women who report smoking at their first prenatal care visit. Physicians will be recruited to volunteer to take part in this randomized study. There are two major phases to the STOP Project - a pretest phase and a formal trial with a built-in pilot study. The objectives of the pretest phase were: 1) to develop the protocol for the STOP study; 2) to develop all study materials (e.g., pamphlets, study forms, manual of operations); 3) to recruit private physicians who will assist in finalizing the study protocol and educational materials; 4) to assist in the development of all quality control procedures; and 5) to train the contractor selected to implement the formal trial in all aspects of the study. At this time, the pretest has been completed and all educational materials for the study have been completed and approved by the physicians and staff participating in the pretest phase. Two contractors, the University of Maryland and Westat, Inc., were selected to execute the pilot and formal trial for the STOP Project. The contract was signed and went into effect on May 15, 1991. The project is presently being piloted in Baltimore, Maryland.