In the period from September 1980 to December 1987, our laboratory measured estrogen (ER) and progesterone receptor (PgR) levels in 960 patients with primary breast cancer. At presentation, 918 of these had no distant metastases. ER as well as PgR were considered positive at values above 10 fmol/mg cytosol protein. All the patients included had been operated on at one of two participating hospitals in the country of North Jutland, and all patients had been checked up in a uniform way at one oncological out-patient department. By applying test for interaction, the PgR was found to be dependent on nodal status. Separate multivariate analyses were carried out for node positive and node negative patients. By this method, size of tumor, histologic grading, and age turned out to be independent prognostic factors for the node negative patients. Independent prognostic parameters for the node positive patients were histologic grading, PgR and postoperative x-ray therapy. The results support the theory that PgR is a better predictor of disease-free survival than ER.