There are conflicting reports about estrogen modulating the activity of nigrostriatal dopaminergic neurons. Furthermore, modulation may be influenced by progesterone levels. Therefore, the clinical effects of sex steroids on parkinsonian symptoms in postmenopausal women with Parkinson's disease (PD) were analyzed in the present study. Patients (n = 12) were under the age of 80, able to perform the motor function tests, and showed no contraindications for estrogen suppletion. Motor function was assessed using the Unified Parkinson's Disease Rating Scale (UPDRS) and a patient interview on subjective changes. In a placebo-controlled, randomized, double-blind trial lasting 8 weeks, no significant dopaminergic effect of estradiol (E2) could be demonstrated, whereas in an open trial phase lasting 2 weeks, progesterone seemed to have an antidopaminergic effect. Several mechanisms are discussed that can account for the fact that we found no effect of E2 on motor functioning in our patients with PD.