To investigate the difference of biochemical characteristics on gsp-positive and gsp-negative growth hormone (GH)-secreting pituitary tumors, 18 GH-secreting pituitary tumors were examined for their clinical characteristics and gsp oncogenes. All patients received the pituitary function combinative stimulating test. It was found that there were no difference in the sex, age, tumor size, course of disease and plasma basal GH levels with gsp-positive and gsp-negative patients. The plasma levels of PRL were increased in most patients (11/18), and the plasma levels of TSH in gsp-positive patients were higher than those in gsp-negative patients (P < 0.05). There was no significant difference in the responses to pituitary combinative stimulating test in gsp-positive and gsp-negative patients. It was concluded that there was little difference in the clinical biochemical characteristics of gsp-positive with gsp-negative GH-secreting pituitary tumors.