1. The aims of the study were to assess the pharmacokinetic parameters and the hormonal effects of the slow-release formulation of the somatostatin analogue (SR-L) in normal male volunteers. 2. Eight healthy males were studied. For the determination of basal values blood was sampled before the injection of vehicle and then every other hour for 8 h in order to measure plasma GH, prolactin (PRL), TSH, free thyroxin (fT4), insulin and glucagon levels. Plasma insulin-like growth factor 1 (IGF-1) levels were measured on a single sample. On day 1 of the study, 30 mg SR-L was administered intramuscularly. Blood was drawn just before injection and then every other hour for a period of 8 h. Thereafter, blood was sampled three times a week for 3 weeks in order to measure lanreotide, IGF-1, TSH, fT4 and PRL concentrations. Plasma GH was determined on days 6 and 11 of the study. 3. Plasma lanreotide concentrations rose to 38.3 +/- 4.1 ng ml-1 2 h following injection. The levels then progressively decreased, remaining above 1.5 ng ml-1 until day 11 and reaching 0.92 +/- 0.28 ng ml-1 2 weeks after injection. The apparent plasma half-life and mean residence time were 4.52 +/- 0.50 and 5.48 +/- 0.51 days respectively. 4. By comparison with the control day, plasma insulin concentrations only decreased 2 h following injection, whereas plasma glucagon did not change at any time. 5. Plasma TSH concentrations were significantly (P < 0.01) reduced from 2 h to day 4 following SR-L injection.2+ '