Estrogen and progesterone receptors are known to be valuable in predicting endocrine responsiveness and aggressiveness of breast cancers. Histochemical detection of these receptors in the heterogeneous cell populations of most tumors would offer new information on heterogeneity as well as making the receptor determination much faster and cheaper and more sensitive and also opening new possibilities for basic receptor research. We have previously shown that most existing histochemical receptor methods probably do not actually detect receptors. Here we have proposed to develop valid cytochemical receptor methods by synthesizing more stable, higher affinity steroid-fluorescein conjugates and subjecting them to regorous testing. A number of new steroid linkages have already been prepared and evaluated. We have also proposed to develop new immunocytochemical receptor methods based on specific monoclonal antibodies against the receptors themselves rather than against their ligands. Partial (several thousand-fold) receptor purification by new affinity chromatography reagents has been applied to both estrogen and progesterone receptors from MCF-7 human breast cancer cells and human uterus, respectively. This will now be followed by preparation of antibodies by the hybridoma technique and the use of these antibodies for receptor detection in frozen fixed sections from tumor specimens. Specificity, sensitivity, and correlation with standard biochemical receptor assays will be regiorously examined for validation of the histochemical method for receptors in breast cancer.