STUDY QUESTIONDoes the expression of LHCG receptor (LHCGR) protein and key enzymes in the androgen biosynthetic pathway differ in normal human versus polycystic ovarian tissue?SUMMARY ANSWERLHCGR and 17α-hydroxylase/17-20-lyase (CYP17A1) protein levels are increased in polycystic ovaries (PCOs).WHAT IS KNOWN ALREADYThe predominant source of excess androgen secretion in women with polycystic ovary syndrome (PCOS) is ovarian theca cells but few studies have directly assessed the presence and abundance of protein for key molecules involved in androgen production by theca, including LHCGR and the rate-limiting enzyme in androgen production, CYP17A1.STUDY DESIGN, SIZE, DURATIONThis is a laboratory-based, cross-sectional study comparing protein expression of key molecules in the androgen biosynthetic pathway in archived ovarian tissue from women with normal ovaries (n = 10) with those with PCOs (n = 16).PARTICIPANTS/MATERIALS, SETTING, METHODSA quantitative morphometric study was performed using sections of archived human ovaries (n = 26) previously characterized as normal or polycystic. The distribution and abundance of LHCGR, CYP17A1, 3β-hydroxysteroid dehydrogenase type 2 (3βHSDII) and 17β-hydroxysteroid dehydrogenase type 5 (17βHSD5) proteins were evaluated by immunohistochemistry and quantified.MAIN RESULTS AND THE ROLE OF CHANCEA higher proportion of theca cells from anovulatory PCO expressed LHCGR protein when compared with control ovaries (P = 0.01). A significant increase in the intensity of immunostaining for CYP17A1 was identified in antral follicles in sections of PCO compared with ovaries from normal women (P = 0.04).LIMITATIONS, REASONS FOR CAUTIONAs the study used formalin-fixed ovarian tissue sections, it was not possible to carry out studies 'in vitro' using the same ovarian tissues in order to also demonstrate increased functional activity of LHCGR and CYP17A1.WIDER IMPLICATIONS OF THE FINDINGSThe data are in keeping with the results of previous studies in isolated theca cells and support the notion of an intrinsic abnormality of theca cell androgen production in women with PCOS.STUDY FUNDING/COMPETING INTEREST(S)The research was supported by a Programme Grant, G0802782, from the Medical Research Council (MRC) UK and by the National Institute for Health Research (NIHR) Biomedical Research Centre based at Imperial College Healthcare NHS Trust and Imperial College London. F.V.C was supported by Capes Foundation (Brazilian Ministry of Education). The authors have no conflicts of interest to disclose.