The development of recombinant somatotropic hormone (STH) creates a prerequisite for a wide application of exogenous stimulation of meat and milk performance of cows and pigs. Reproduction effect and its mechanism is till now restricted by a lack of complex information though there are several studies of principal character and basic effects of STH on reproduction process are also known. The result of some experimental studies, quoted in scientific literature, was a hypothesis that STH effect is accompanied by increased production of so-called insulin-like growth factors. Moreover, it is known that these factors have a steroidogenic effect. A hypothesis of STH action, just by means of insulin-like growth factors, was expressed on the basis of the above mentioned fact. Our study was aimed at the analysis of the effect of recombinant porcine somatotropic hormone (rpSTH, Research and Development, Pittman-Moore, Inc.; Terre Haute, Indiana, the U.S.A., LG-COMP-1776/93) on the dynamics of progesterone, cAMP, cGMP concentrations in the blood plasma of sexually mature gilts with surgically introduced permanent canula in v. jugularis. Gilts of early and medium follicular stages of the oestrous cycle (found laparoscopically) without any developmental or any other anomalies in reproductive organs. Blood samples were collected each 15 minutes in the period of 30 minutes before and 150 minutes after rpSTH application (5 mg per gilt). The control of gilts was administered 0.9% NaCl solution under the same conditions. Blood plasma samples collected and processed were stored not earlier than after radioimmunoassay of substances. A part of the study was to analyze different rpSTH doses (1-100,000 ng/ml) on granulosis cells on gilts' ovaries obtained after slaughtering of sexually mature gilts without any visible changes in the reproductive system. Granulosis cells were separated after aspiration of follicles of the size 2 to 5 mm without marked paleness, after thrice resuspending in essential cultivation medium TCM 199 and centrifugigng (g = 200). Followed the last straining of supernatant the cells were resuspended in the cultivation enriched medium TCM 199. 2 ml of cell suspension in the cultivation medium with known counts and viability of cells (10(6) in 1 ml and 75-95% vitality) were cultivated in defined conditions as a basic unit of the experiment. Resulting concentrations of analyzed hormones were determined on the basis of production activity of cells and statistically assessed by ANOVA test.(ABSTRACT TRUNCATED AT 400 WORDS)