Peripheral benzodiazepine receptors have been evidenced in human normal prostate and prostatic nodular hyperplasia using [3H]Ro 5-4864 and [3H]PK 11195. Binding of both radioligands was found to be saturable. In normal and pathologic tissues, Scatchard analysis revealed a single population of binding sites. KD values of [3H]PK 11195 in normal and hyperplastic prostates were 14.6 +/- 5.6 and 12 +/- 2.42 nmol/l with Bmax of 12,155 +/- 1,328 and 13,924 +/- 2,454 fmol/mg protein, respectively. Using [3H]Ro 5-4864, the value of Bmax was similar (13,630 +/- 1,878 fmol/mg protein), but its affinity was 15 times lower when compared to [3H]PK 11195. Human prostatic nodular hyperplasia is not associated with a change in the density of peripheral benzodiazepine receptors.