Forty one pituitary adenomas excised surgically were immunostained to reveal pituitary hormones and chromogranin A (CgA). In 23 patients, plasma CgA concentration was determined before surgery by ELISA method. The CgA immunopositivity was found in 70.7% of investigated tumors. It was observed in all tumors of gonadotropinoma type and in the majority of null cell adenomas. Elevated (>18 U/L) plasma CgA concentration was observed in approx. a half of the examined patients, being more frequent in gonadotropinomas and null cell adenomas. It may have some, although limited, diagnostic value in these types of pituitary tumors.