Described here is an immunohistochemical technique using the commercially available monoclonal progesterone receptor (PR) antibody KD 68 in routinely fixed and paraffin-embedded breast carcinomas and lymph node metastases. The authors' technique is compared with several incubation variations. The method applying the primary antibody in a dilution of 1:10 overnight followed by a biotinylated second antibody showed the best results when Triton X-100 was added to the buffer. Using this method, comparison with the results on frozen sections of 34 breast carcinomas yielded a significant concordance of 94%. Correlation between the results on paraffin sections and those obtained by the standard dextran-coated charcoal cytosol assay was 80%. The value of the method for predicting endocrine therapy response was shown in 20 patients. Thus the reliability of the method has been demonstrated and was applied on 151 lymph node metastases and the corresponding primary breast carcinomas from 50 patients. Generally PR content in the metastases was lower than in the primary tumors (p < 0.001). This finding indicates that evaluation of PR in lymph node metastases should be included in the decision for endocrine therapy of breast cancer.