We investigated the effect of prostatic inflammation on prostate-specific antigen (PSA) and per cent-free PSA levels changing after antibacterial therapy. We evaluated 48 patients whose PSA levels were between 4 and 10 ng/ml, without any suspicious findings on digital rectal examination, with no infection findings in urine analysis. Prostatic inflammation was assessed with prostatic massage. All the patients were given antibiotic therapy for 3 weeks. Patients were re-evaluated 3 weeks after antibacterial therapy with PSA (free/total) and urinalysis. Ten core biopsies were taken with transrectal ultrasound. No differences were found in terms of age, pre- and post-treatment PSA, and PSA varying between patients with and without inflammation in the prostatic massage. In 18 patients, PSA decreased below 4 ng/ml. Prostate cancer was found in 10.8% of the patients with PSA between 4 and 10 ng/ml and none of the patients with PSA values below 4 ng/ml. We suggest an antibiotic therapy for 3 weeks without regarding inflammation findings when PSA is in the gray zone, for biopsy decision.