Prostate specific antigen (PSA) is the most important tumour marker which, used routinely, proved to have a positive correlation with tumour volume and pathological stage. To evaluate the relationship between serum PSA and histologic grading of prostatic carcinoma, preoperative PSA determinations were made in 25 patients with prostatic cancer. Biopsy materials were evaluated and the Gleason scores were adjusted for histologic grading. The higher values of PSA were proportional to the Gleason scores of the primary prostatic biopsy.