Since the introduction of treatment by in vitro fertilization/embryo transfer (IVF-ET) in humans, a harmless approach to identifying the ovum with a greater chance of producing an implantable embryo has been sought worldwide. Our previous studies indicated a high correlation between degree of follicular maturation and benzodiazepine (BZ) receptor density in rats. We hypothesized that if such a correlation existed in humans, the latter might be used to evaluate degree of follicular maturation and, consequently, its corresponding oocyte competence. We used [3H]PK 11195, a ligand selective to peripheral BZ receptors, to determine their density in human granulosa-lutein (G-L) cells. [3H]PK 11195 bound to G-L cells with high affinity in a saturable manner. Scatchard analysis revealed the presence of a single population of receptors. The average equilibrium dissociation constant and maximal number of receptors (Bmax) measured in G-L cells were 3.4 +/- 0.2 nM and 608 +/- 61 fmol/mg protein, respectively. In G-L cells obtained from individual follicles, a significant increase in the specific binding to peripheral BZ receptors was noted in G-L cells of follicles yielding oocytes at an advanced stage of cumulus maturation or oocytes competent for fertilization and subsequent cleavage. When G-L cells were pooled from all the follicles of each individual woman, the average Bmax value of [3H]PK 11195 in G-L cells was 900 +/- 127 fmol/mg protein in women who conceived, which was 80% higher (P less than 0.01) than in women who did not conceive.(ABSTRACT TRUNCATED AT 250 WORDS)