The aim of the study was to determine the inhibitory effects of somatostatin analogues with relative specificity to somatostatin receptor subtype 2 (SSTR2) (BIM-23197), subtype 5 (SSTR5) (BIM-23268), and their combination on GH and PRL secretion in acromegalic adenomas in vitro. Three types of answer were observed: 1. In one resistant adenoma no inhibition was achieved. 2. The GH secretion in six adenomas was suppressed significantly more (p < 0.01 or p < 0.001 using Mann-Whitney U-test in concentration range of 10(-12) to 10(-8) mol/l) with SSTR2 specific analogue BIM-23197 with no additive effect of compounds combination. 3. In three adenomas the potency of BIM-23197 and BIM-23268 was almost equal and the combination of these SSTR2 and SSTR5 specific compounds had statistically significant additive effect (p < 0.05 or p < 0.01 in concentration range of 10(-12) to 10(-8) mol/l). PRL secretion of five adenomas was more suppressed with SSTR5 specific BIM-23268 (statistically significant in concentrations 10(-10) to 10(-8) mol/l). In conclusion the somatostatin analogue BIM-23268 had an additive effect on suppression of GH secretion in a subset of adenomas, where both SSTR2 and SSTR5 were involved. This effect was not observed in the majority of tumours, where the inhibitory effect seems to be mediated via SSTR2 only.