The aim of the present study was to examine the correlation between the immunohistochemical findings and the serum markers for neuroendocrine (NE) cells in patients with carcinoma of the prostate. Preoperative serum values of chromogranin A (CgA), chromogranin B (CgB), pancreastatin (Pst), neuron-specific enolase (NSE), and prostatic specific antigen (PSA) were determined in 22 patients. The tissue specimens were obtained by a palliative transurethral resection of the prostate (TURP) because of urinary outflow obstruction. Immunohistochemistry was performed by using antibodies against CgA, CgB, NSE,.serotonin, thyroid-stimulating hormone (TSH), and somatostatin. Tumor cells with NE differentiation were found in 91% of the cases. No patient had elevated serum values of NSE, despite the presence of NSE-positive tumor cells in 77% of the tumors. Neither did CgB in serum correlate with the immunohistochemical findings. Elevated serum values of CgA were found in 59% of patients. A positive correlation between the number of CgA-staining cells and the serum values of CgA was found, as seven out of eight patients with groups of CgA-positive tumor cells had elevated serum values of CgA. We conclude that CgA, in contrast to NSE, CgB, and Pst, seems to be a useful serum marker in predicting the extent of NE differentiation in prostatic tumors.