Androgen-binding protein (ABP) and oxytocin (OT) are among the factors that control smooth muscle proliferation and tumour growth through oxytocin receptor (OTR). A close functional interaction of OTR and caveolin 1 has been shown to modulate cell growth and proliferation. We investigated samples from 10 patients (mean age 68.3) who underwent transurethral prostate resection because of benign prostate hyperplasia (BPH) by immunohistochemistry. Post-mortem prostate samples of three young men (age 18, 28, 33) were used as controls. Tissue samples were embedded in epoxy resin and cut into serial 1 mu m sections for colocalization of ABP, OTR, proliferation marker p21 and caveolin 1. ABP was found in stroma of the smooth muscle cells in all studied samples. OTR staining occurred in most of these cells in BPH while controls contained only scattered cells positive for OTR. There were no apparent differences in immunostaining for p21 while immunoreactivity for caveolin 1 was observed in most cells in BPH and only in few cells in controls. Caveolin 1 was mostly colocalized with ABP and OTR in BPH samples while controls did only occasionally show this colocalization. Our observations indicate an interaction of ABP and OTR, associated with caveolin 1, which may account in part for known non-genomic actions of gonadal steroids. Androgen dependent prostate growth in BPH may be linked to these mechanisms.