Nine patients with polycystic ovary syndrome (PCOS) and exaggerated serum level of 17-hydroxyprogesterone (17-OHP) response to gonadotropin (GnRH) agonist stimulation, and seven patients with PCOS, but normal 17-OHP response have been analysed for possible linkage of PCOS with genetic defects on the 17 alpha-hydroxylase/17,20-lyase gene (CYP17). A portion of the regulatory and the entire coding domain for this enzyme have been analysed by PCR-SSCP analysis. Samples have been also screened for the previously reported -34 bp polymorphism, which creates a new SP1-type promoter site, but was excluded as the primary genetic defect. We have varied gel concentrations, reduced running temperatures, added glycerol to polyacrylamide gels and performed electrophoresis on longer gels in order to improve the resolving power of SSCP. Screening of the CYP17 gene revealed no mutations associated with the disease in the examined group of patients. Also, the -34 bp polymorphism proved to be equally distributed among patient and control samples, which in our case were non-related. The results indicate that, when germline mutations in question, CYP17 may be excluded as a candidate gene for these subtypes of PCOS.