Breast cyst disease is a common problem in women. In the last decade, several studies have focused on the biochem. anal. of breast cyst fluids (BCFs). The present study confirms the presence of polypeptides, as epidermal growth factor (EGF), conjugated androgens, sometimes at very high concentrations, when compared with the levels found in circulating plasma. It is also found a significant direct correlation between dehydroepiandrosterone sulfate (DHEA-S) and androstane-3α, 17β-diol glucuronide (3α-Adiol G) (r = 0.8744) and with the EGF (r = 0.8949), and an inverse correlation between 3α-Adiol G and Na/K (r = -0.6592). It is also determined the levels of human chorionic gonadotropin (hCG) measured with a chemiluminescent detection system. It is found a neg. correlation between this glycoprotein and the levels of DHEA-S, 3α-Adiol G and EGF and a pos. correlation with Na/K. The presence of hCG in BCFs, generally considered as a tumor marker, suggest the possibility that this hormone could be de novo synthesized by the epithelial cells lining the cysts.