Free (n = 432) and total (n = 387) prolactin receptors (PRL R) (after 3 M MgC12 desaturation) as well as estradiol (ER) and progesterone receptors (PgR) were measured in 547 breast cancer patients surgically treated in the Oscar Lambret Centre. Free PRL-R were found in 43% of the cases, total PRL R in 72%, ER in 81% and PgR in 55%. A statistically significant correlation was found by the Spearman test between ER on the one hand free PRL R (P less than 0.02) and total PRL R (P less than 0.001) on the other and between PgR on the one hand, free PRL-R (P less than 0.05) and total PRL R (P less than 0.01) on the other. A linear correlation test could be done on subgroups of values, excluding zero values, of each of the receptor type; a statistically significant correlation could be found between ER and total PRL R (P less than 0.001) and between PgR and total PRL R (P less than 0.05). These results confirm, on a large series, the relation between PRL R, ER and PgR in breast cancer.