Elevated concentrations of peptide hormones have been described previously in human breast fluid. In the current study, the levels of cortisol, progesterone, testosterone, dihydrotestosterone, androsterone, androsterone sulfate, dehydroisoandrosterone, dehydroisoandrosterone sulfate, estradiol, estrone, estradiol sulfate, and estrone sulfate were measured. The levels of the four 17-ketosteroids and the two estrogen sulfates were markedly elevated over the plasma level, while that of the other compounds was the same or only slightly higher than the plasma levels of the same compounds.