Treatment of the rats with actinomycin D or actidione for 48 hr prior to sacrificing animals resulted in a significant reduction of DNA synthesis and the activity of DNA polymerase in testosterone-stimulated ventral prostate on the 4th day after testosterone administration. Under the same treatment of inhibitors, increase of the rate of 5α-reduction of testosterone on the 4th day after testosterone treatment was lower than that in the from the animals treated with testosterone alone. However, some elevation of the of 5α-reduction was observed between the 2nd and 4th day after testosterone treatment, regardless of the administration of actinomycin D or actidione. Treatment of mitomycin C did not make a significant difference in the increase of the rate of 5α-reduction DNA polymerase activity.It was concluded that the mode of increase of rate of 5α-reduction was different from that of DNA polymerase activity on the 4th day after testosterone treatment, and that some part of elevation of the rate of 5α-reduction was independent of the treatment of metabolic inhibitors.