Receptor content of human decidua in early pregnancy (weeks 6-12) was investigated. Fifty-three tissue samples were obtained from voluntary patients undergoing abortion and whose gestational age range from 6 to 12 weeks. Blood samples were drawn at the time of operation in order to measure circulating estradiol (E) and progesterone (P) concentrations. Tissue samples underwent first histological confirmation and then were analyzed for receptor content by immunohistochemistry (IH) and by the conventional ligand binding technique (LBA). Estrogen receptors (ER) appeared to be always undetectable by IH (53 samples). LBA measured a significant amount of ER (> 10 fmol/mg) in two samples, borderline values (3-10 fmol/mg) in 6 and no binding in the other three. No relation was apparent between PR levels and either gestational age or blood P concentration. ER were possibly downregulated by the high E levels, and their synthesis inhibited by the high P levels.