The experiments were designed to test the possibility to induce a down-regulation of pituitary GnRH-receptors and hence a suppression of oestrus by application of a long term deslorelin implant in female rats. Sixteen non pregnant female rats were randomly divided into two equal groups. The eight rats of the implant group (DESL) were subcutaneously implanted with long acting deslorelin implant, an analog of GnRH, at the dose of 4.7 mg, to inhibit oestrus. No treatment was applied to control group (CON). One adult male rat was added per cage of DESL and CON females after six weeks. Conceptions were diagnosed by inspection, palpation, and ultrasonography for one year. Conception rates were 0% and 100% in DESL group and CON group, respectively (P<0.001). An influence of the deslorelin insertion on the concentrations of progesterone and oestradiol - 17 beta was determined. Average hormone concentrations were statistically different between groups (P<0.01). In conclusion, the subcutaneous implantation of 4.7 mg of deslorelin is a practicable method for suppressing oestrus in rats. Further investigative studies will be required to determine upper time limit of down-regulation duration by deslorelin.