High performance liquid chromatography in reversed-phase system was used to control the synthesis ofFinasteride{17β (N-tert-carbamoyl)-4-aza-5α-androst-1-ene-3-one} - the drug used in the therapy of prostatic carcinoma. The objective of these investigations was the finding of such composition of mobile phase which would separate the semi-products obtained in individual stages of synthesis from final products and UV detection at 210 nm. For this purpose we adopted the method of triangle optimisation.