Prostate samples from 41 patients with acute on chronic prostatitis, benign hyperplasia, chronic prostatitis or adenocarcinoma were assayed for cytosolic retinoic acid binding protein (cRABP). Binding protein was detected in all samples. Scatchard analysis revealed dissociation constant values of 15.0-31.8 nM and maximum binding capacity of 5.2 +/- 2.0 (S.E.) pmol/mg protein. Using sucrose density gradient centrifugation, cRABP was quantitated and values varied from 1.2 to 12.5 pmol/mg protein. High levels (greater than 3.5 pmol/mg protein) were found in 28/41 samples. There was no correlation between the cRABP binding/mg protein and the volume (%) of glandular tissue (compared with stroma). While there was no significant difference in the quantities of cRABP in the different disease groups, there was a tendency for a progressive increase from acute on chronic prostatitis to chronic prostatitis, the highest levels being present in carcinoma.