From March to December 1975, 496 patients were studied to compare the safety and effectiveness of menstrual regulation (MR) performed with a Karman hand syringe and first trimester abortion performed with an electric vacuum aspirator. All procedures were done on an outpatient basis. The complication rate for the MR patients was significantly lower than that for the other first trimester abortion patients. Study results indicate that MR with the Karman syringe is a safer, simpler and less costly procedure than first trimester abortion with the electric vacuum aspirator. Further research and study are necessary to determine the effect of the initial and repeat MR procedures on women's menstrual patterns and future pregnancies, including any subsequent prematurity, stillbirths and Rh immunization.