BACKGROUND The population exposed to repeated cycles of gonadotropin-releasing hormone analogue treatment before in vitro fertilization is growing rapidly. Sex steroids have been shown to induce changes in carbohydrate metabolism. In view of the effect of gonadotropin-releasing hormone analogues on sex steroid levels, it seems of interest to investigate carbohydrate metabolism following treatment with these compounds. OBJECTIVE Our purpose was to assess possible changes in glucose tolerance following administration of the long-acting gonadotropin-releasing hormone and analogue, D-Trp6 LH-RH. METHODS A 3-hr oral glucose tolerance test with 100 g glucose was performed on all patients, before and after 6 weeks of treatment. RESULTS No significant changes in either glucose tolerance or insulin levels following treatment with D-Trp6 LH-RH were demonstrated in the group of 25 women investigated. CONCLUSIONS With respect to carbohydrate metabolism, D-Trp6 LH-RH may safely be administered to healthy women. Further studies are still required to assess the safety of this GnRH analogue when treating potentially diabetic and diabetic patients.