Although prostatitis is a common problem the diagnosis is still controversial despite the availability of a wide variety of diagnostic tools. In fact, there is still no accurate method of localizing the infected tissue. The aims of the present study were to assess whether 111In labelled leukocytes (ILLs) accumulated in the infected tissue of acute prostatitis and if such uptake responded to treatment. We prospectively studied 10 adult male patients who had community acquired prostatitis and compared them with six male patients who had urinary tract infections but without prostatitis. An initial urinary culture and two blood cultures were carried out for each patient. All patients were followed up for 8 weeks after therapy was completed. Pre- and post-treatment scintigraphies were performed. Before treatment, all patients with prostatitis showed uptake of ILLs in the prostate area. After the patients had completed treatment with antibiotics, the scintigraphy results showed no uptake in the prostate area in 9/10 patients. The remaining patient showed a marked decrease in the uptake of ILLs. None of the six patients with urinary tract infection showed ILL uptake in the prostate region. It is suggested that ILLs could be useful for detecting acute prostatitis, especially in clinically ambiguous patients with urological infections. Furthermore, scintigraphy with 111In labelled leukocytes could help to determine the most appropriate course of therapy.