The substudy was a population-based experiment with White, Black, and Hispanic pregnant women whose continued smoking made them ineligible for randomization into the parent study. It was unique in focusing on heavier, more addicted pregnant smokers. PANDA research sites and protocols offered a special opportunity for a low cost test of a disseminable intervention which this project team was uniquely qualified to design and implement. The new intervention, One- to-One, used telephone counselors to assess the counselee's stage in the change process and give stage-appropriate messages, using established techniques of motivational interviewing. Between the two counselor calls spaced 10 days apart, counselees received personalized written feedback and suggestions. The primary aim, increasing quitting during pregnancy, was assessed by unobtrusive urine samples taken during prenatal visits in the ninth month and identified only by study group.