In a study involving 50 breast cancer tumours, we compared two oestrogen receptor (ER) detection methods developed by us--a microplate immunoenzymometric assay (EIA96) and an immunohistochemistry kit (HistoCIS-ER)--with the radioligand assay (RLA), the Abbott immunoenzymometric assay ER-EIA and the reverse transcriptase polymerase chain reaction technique (RT-PCR). Among the three ER protein cytosolic assays (EIA96, ER-EIA and RLA), the two EIAs showed the best agreement (y = 1.086x - 7.840; r2 = 0.876). At the calculated optimal cut-off values (8 and 14 fmol mg(-1) protein for EIA96 and RLA respectively), EIA96 was more sensitive than RLA (0.94 for EIA96, 0.88 for RLA), but slightly less specific (0.82 for EIA96, 0.94 for RLA). The Cox logistical regression model applied to EIA96, RLA and RT-PCR showed that EIA96 discriminated the best between ER-EIA+ and ER-EIA- samples. The RT-PCR technique and HistoCIS-ER both had a positivity-negativity concordance of 86% with EIA96.