In contrast to the situation in invasive breast carcinoma, there are only few reports on the levels of receptors for estrogen (ER) and progesterone (PgR) in pre-invasive (in situ) breast carcinoma. In the present study ER and PgR levels were analyzed in 57 in situ human mammary carcinomas using a quantitative enzyme immunoassay method. Intraductal carcinoma was the dominating histopathological subgroup (75%). Within this subgroup the non-comedo and comedo variants comprised 66 and 34 percent respectively. Intralobular and papillary in situ subtypes were the second most frequent subgroups, representing 11% each. Using a cut-off level of 0.05 fmole/microgram DNA to define receptor poor and rich tumors we found that thirty-one out of the 57 cases (54%) were ER-rich. In the ER-rich tumors the receptor levels varied between 0.05 and 6.50 fmole/microgram with a mean concentration of 0.80 fmole/microgram DNA. Fifteen of 51 (30%) tumors were classified as PgR-rich tumors in which the levels ranged between 0.05 and 2.90 fmoles/microgram DNA, with a mean concentration of 0.45 fmoles/microgram DNA. Two thirds of the non-comedo, lobular and papillary variant were ER rich. A majority (80%) of comedo tumors were ER poor. Our findings show that 54% of in situ breast carcinomas have the molecular prerequisites for response to antiestrogen therapy which is of interest when planning adjuvant treatment protocols.