OBJECTIVE The use of GnRH agonists for desensitization of the pituitary is widespread in gynaecological practice. For indications such as contraception and treatment of uterine leiomyomata partial desensitization may suffice. With respect to partial desensitization of the pituitary we have addressed three basic questions: (1) Is the degree of pituitary desensitization dependent on the dose of agonist used? (2) What is the optimal way to measure the degree of pituitary desensitization? (3) Is it possible to create a standard to express the degree of pituitary desensitization?DESIGN AND PATIENTS Twenty‐four women were randomized into 4 groups of 6 women. To achieve pituitary desensitization, the groups received 0.1, 0.25, 0.5 and 1.0 μg/min GnRH respectively, for 6 weeks.MEASUREMENTS Pituitary desensitization was measured by gonadotrophin levels and responses to a 100‐μg bolus of GnRH and an oestradiol benzoate challenge‐test.RESULTS The level of LH and the responses of LH and FSH to the GnRH challenge showed significant dose‐dependent suppression. Multiple regression indicated the LH response to the GnRH challenge was the best way to measure pituitary desensitization. From the LH responses to the GnRH‐challenge a ‘standard curve’ was established for the assessment of the degree of pituitary desensitization.CONCLUSION The LH response to the GnRH challenge test is the best available measure of pituitary desensitization du