Recently a growth hormone releasing factor (GRF) has been isolated from a pancreatic tumor of an acromegalic patient. This peptide with 44 aminoacids (hpGRF1-44) has been synthesized and has been shown to have growth hormone releasing property in vivo and in vitro. We have examined the growth hormone response to synthetic hpGRF1-44 in 10 normal male and 5 normal female subjects, in 4 patients with active acromegaly and in one patient with hypothalamic pituitary insufficiency. After the injection of 100 micrograms hpGRF1-44, growth hormone increased in all normal controls within 5-15 min from a mean basal level of 0.64 +/- 0.06 ng/ml +/- SE to a peak of 16.7 +/- 3.3 ng/ml 30 min after hpGRF1-44. No significant side effects were recorded. All other anterior pituitary hormones showed no increase after hpGRF1-44. In addition, no significant change of blood glucose, pulse rate or blood pressure was recorded after hpGRF1-44. In 4 normal subjects the growth hormone response to 100 micrograms hpGRF1-44 was compared with the response to insulin-induced hypoglycemia. There was no significant difference between the maximum increase of growth hormone after hpGRF1-44 and hypoglycemia. In 3 out of 4 patients with active acromegaly 100 micrograms hpGRF1-44 led to a clear-cut increase with a peak value at 15 min, whereas one patient with postoperative active acromegaly showed no GH increase after 100 micrograms hpGRF1-44. One acromegalic was tested before and 6 weeks after incomplete transsphenoidal surgery with the same response from a lower basal level after surgery as before.(ABSTRACT TRUNCATED AT 250 WORDS)