Endogenous cortisol levels were measured by radioimmunoassay in 140 primary and 31 metastatic human breast cancer specimens. The adjacent normal breast was assayed in 15 cases. Mean values for normal breast were 17.3 ng/g tissue. Significantly higher levels were found in cancer tissue. Primary lesions contained 26 ng/g and metastases 32.5 ng/g cortisol. These results lend support to our previous data on increased cortisol binding activity in human breast cancer.