The majority (72 percent) of U.S. residency programs in obstetrics and gynecology include first-trimester abortion techniques in their training. Programs affiliated with public hospitals or with private non-Catholic institutions are the most likely to provide such training, while Catholic-affiliated training programs and those at military hospitals are the least likely to do so. Approximately 23 percent of institutions include abortion training as a routine part of residency, and 50 percent offer it as optional training. The 28 percent of residency programs that offer no abortion training represents an almost fourfold increase since 1976. Although more of the large programs affiliated with public hospitals now include such training as a routine part of their residency programs, fewer of the private non-Catholic programs--where the largest proportion of residents are trained--do so. Consequently, the number of residents exposed to abortion training may have declined slightly over the past decade. Little difference exists between the proportion of programs that offer training in first-trimester techniques and the proportion that train in second-trimester techniques. Nine percent of programs report that all residents participate in first-trimester abortion training, and another 56 percent report that at least half of their residents do so. The participation rate is linked to the expectations of the program: Approximately 88 percent of programs that routinely incorporate abortion techniques in their training report that from one-half to all their residents participate, compared with about 55 percent of programs that offer the training as an option. Approximately 82 percent of programs teach abortion techniques up to at least 20 weeks' gestation.(ABSTRACT TRUNCATED AT 250 WORDS)