The effects of two newly developed triphasic preparations with a sequence of 6/5/10 and a reduced content of the total dose of oestrogen per cycle on the parameters of cycle function were studied in 10 young women with normal phasic cycles using a randomized trial design. Cervical function, spinnbarkeit and crystallisation of cervical secretion and the karyopyknotic index were monitored and LH,E2 and progesterone levels in serum radioimmunologically determined in a pretreatment control cycle, the immediately following 1st treatment cycle, the 3rd treatment cycle and a subsequent treatment-free cycle. Both preparations brought about suppression of ovulation already in the 1st treatment cycle with the periphery (cervical barrier) greatly reduced but still reactive. The results of the study show that by adapting the ratio of active substances to the phases of the normal cycle, not only good cycle control and tolerance are achieved but also inhibition of ovulation.