This study has evaluated the behaviour of 3 alpha-androstanediol glucuronide (3 alpha-diol G) in 170 women of whom 85 had polycystic ovary syndrome (PCOS), 35 had idiopathic hirsutism (IH) and 50 had regular cycles (control group). Of the women with PCOS. 45 were hirsute (PCOS-H) and 40 were non hirsute (PCOS-NH). Women in the control group were not hirsute. Hirsutism was assessed by the same physician using the Ferriman-Gallway score. The body mass index (BMI) was estimated in all of the women. Plasma concentrations of 3 alpha-diol G were elevated only in hirsute patients, both with PCOS and with IH. Even in PCOS-NH, concentrations of 3 alpha-diol G were higher compared with controls (P < 0.001), but significantly lower (P < 0.001) than those of the PCOS-H and of the IH groups. The behaviour of 3 alpha-diol G was not affected by BMI.