Serum and urinary measurements of 3 alpha,17 beta-androstanediol glucuronide (3 alpha-diol G) reflect peripheral androgen action and have been useful clinically. This study was designed to compare these levels in hirsute women, normal premenopausal and postmenopausal women, and in men and to correlate each measurement with skin 5 alpha-reductase activity (5 alpha-RA), an excellent correlate of androgenicity. Although serum 3 alpha-diol G values were similar in premenopausal and postmenopausal women, values were higher in hirsute women and in men. This pattern was similar for urinary 3 alpha-diol G but with greater overlap in values between hirsute and nonhirsute women and men. Serum 3 alpha-diol G showed a highly significant correlation with levels of genital 5 alpha-RA (r = 0.839, P less than 0.001), whereas urinary 3 alpha-diol G did not correlate. Serum and urinary 3 alpha-diol G also did not correlate with one another (r = 0.03). These data suggest that while both serum and urinary 3 alpha-diol G may be useful clinically, serum 3 alpha-diol G appears to correlate better with androgenicity and 5 alpha-RA. It is suggested further that the sources of serum and urinary 3 alpha-diol G may be somewhat different.