The purpose of this study was to determine which of the 6 indirect tests for ovulation used would give results most consistent with each other and with accepted views as to the time of occurrence of this phenomenon, in the belief that synchronicity of occurrence would confirm a given test''s reliability whereas irregularities would tend to discredit a test. Twenty cycles of 5 subjects were analyzed. using, concurrently, 4-6 of the following tests, gonado-trophin assay, estrogen assay, pregnanediol assay, vaginal smear, body temp. and subjective experience. Daily, 24-hr. specimens of urine were collected and assayed for the hormones mentioned, using standard methods. The results are presented in 2 groups of graphs; the first group makes possible a comparison of hormonal assay results, body temp. and vaginal smears, of all cycles, on the basis of data of the same degree of accuracy. Certain cycles were assayed more thoroughly and the 2d group of graphs presents results of greater quantitative value. It was found that subjective experiences are valueless as tests for ovulation; that body temp. fluctuations are not sufficiently regular nor clear-cut to be reliable; that uniformity of hormonal assays and vaginal smear results reinforces confidence in the merits of each and a certain sequence of events appears typical of the normal cycle; and that because of its sharpness and apparent close association with ovulation, the gonadotrophin peak occurring in the mid-interval is the most reliable of indirect tests for ovulation.