We investigated the 24-hour mean blood glucose and serum insulin (IRI), C peptide (C pep) and glucagon concentrations before (pre) and after (post) continued treatment with octreotide (100 mcg three time daily by s.c. injection) in a woman, 68 years old, affected by a nine years long benign insulinoma. The blood pool to dose 24-hour mean glucose and all hormone concentrations was obtained by equal quantities of blood samples taken every 2-hour over 24-hour. The IRI, C pep, glucagon, glucose circadian pattern and IRI/glucose ratio were determined on remaining blood portions. After continued treatment with octreotide was significantly reduced the exaggerated and inappropriate insulin (pre = 77.08 +/- 23.6 microUI/ml; post = 15.19 +/- 2.3 microUI/ml; p < 0.001) and C pep secretion (pre = 4.17 +/- 0.4 ng/ml; post--1.64 +/- 0.04; p < 0.001), while the blood glucose levels were significantly elevated (pre = 40.46 +/- 3.1 mg/dl; post = 132.46 +/- 6.9 mg/dl; p < 0.001). Also glucagon levels were significantly inhibited (pre = 73.53 +/- 12.19 pg/ml; post = 46.80 +/- 9.1 pg/ml; p < 0.05). The long-acting somatostatin analogue has improved a lot IRI/glucose ratio (pre = 1.9 +/- 0.4; post = 0.12 +/- 0.04; p < 0.001). A significant positive correlation was found between IRI and C pep before (r = 0.93; p < 0.001) as well after octreotide treatment (r = 0.85; p < 0.001). A significant positive correlation (r = 0.69; p < 0.008) between IRI and glucose was observed only after octreotide treatment.(ABSTRACT TRUNCATED AT 250 WORDS)