A clinical study was performed to determine the efficacy of the Pipelle in obtaining endometrial samples to be analyzed for luteal function. Patients' tolerance of this instrument and their willingness to undergo subsequent biopsies were also ascertained. An endometrial sample was obtainable from 1,278 women with the Pipelle, whereas 52 required the Novak curette and in 60 the sample could not be obtained with either instrument. Thirteen percent of the patients biopsied with the Pipelle stated that they would not allow a second such procedure to be performed. One percent of the samples were deemed inadequate for hormonal reading. The Pipelle seemed to be a safe, minimally traumatic method of sampling the endometrium for hormonal evaluation.