A luteinizing hormone-releasing hormone (LH-RH) analogue was administered for 3 to 32 months to 15 prostatic cancer patients in stage B-D (B:3, C:8, D:4). Intratesticular, intratubular and prostatic androgen levels were measured by radioimmunoassay before and after LH-RH analogue therapy. The measurement of serum prostatic acid phosphatase (PAP) and prostatic specific antigen (PA) levels was also conducted. Thereafter, we assessed the effect of the LH-RH analogue on androgen levels and the relation of prostatic tissue 5 alpha-dihydrotestosterone (DHT) level to the clinical response. The results were as follows: 1) Johnsen's mean germinal epithelium count was significantly decreased from 7.7 +/- 2.1 (mean +/- S.D.) to 4.3 +/- 2.3, and the wall thickness of seminiferous tubules was increased from 5.93 +/- 1.31 to 11.9 +/- 3.64 microns. 2) Plasma testosterone (T), intratesticular and intratubular androgen levels were significantly decreased (plasma T: from 4.40 +/- 1.84 to 0.61 +/- 0.32 ng/ml, intratesticular T: from 335.3 +/- 170.3 to 4.6 +/- 3.8 ng/g.t.w., DHT: from 25.3 +/- 11.7 to 3.7 +/- 2.7 ng/g.t.w., intratubular T: from 50.8 +/- 36.6 to 0.10 +/- 0.99 ng/g.t.w. and DHT: 7.54 +/- 3.20 to 0.63 +/- 0.90 ng/g.t.w.). 3) Crude nuclear DHT levels in prostatic tissue fell from 15.3 +/- 9.3 (N = 8) to 0.37 +/- 0.54 pg/mg protein (N = 3) and the level was non-detectable in 5 of 8 cases. 4) Complete remission was achieved in 1 patient, partial response in 5, objective stable in 8, and objective progression in 1 patient, according to Shimazaki's criteria.(ABSTRACT TRUNCATED AT 250 WORDS)