The availability of RIA to measure the pituitary gonadotropins and ovarian sex steroids has greatly helped in the development of tests of hypothalamic-pituitary-ovarian function. The use of estimates of basal gonadotrophin and sex steroid hormones together with dynamic tests such as the LH-RH test, oestrogen provocation test, clomiphene tests and exogenous gonadotrophins can now test the integrity and functional capacity of each of the components of the HPO axis. Figure 4 demonstrates how these tests can be used in a logical sequence to investigate patients with a disorder of the HPO axis after having first excluded any other endocrine abnormality. Screening of serum for elevated levels of gonadotrophins, prolactin and progesterone is an important initial step. Interpretation of the oestrogen provocation and clomiphene tests requires a normally functioning pituitary gland and hence the response to an LH-RH test also plays a ket role. The flow chart also demonstrates the points at which specific ovulation induction treatment can be instituted and should be useful in saving patient and doctor investigative time. Using these types of tests it should be possible to reclassify disorders of the HPO axis on the basis of their underlying pathology.