58 women with raised serum prolactin levels and normal hypophyseal X-ray parameters were subdivided into three groups according to the serum prolactin level (16 to 40, 41 to 80, greater than 80 ng/ml). In addition to the determination of LH, FSH, oestradiol, progesterone and testosterone in the serum and thyroid diagnostic procedures the following hormonal tests were performed: 1. response to gestagen; 2. response to clomiphene; 3. Gn-RH-test for hypophyseal function; 4. ovarian response to administered gonadotropins (only in cases with prolactin levels administered gonadotropins (only in cases with prolactin levels greater than 80 ng/ml). The grade of menstrual cycle disorders depends on the severity of the observed hyperprolactinaemia. Slight disorders like luteal phase insufficiency, anovulatory cycle and oligomenorrhoea are associated with low- or medium-grade hyperprolactinaemia. Mainly secondary, but also primary amenorrhoea is found in cases with higher serum prolactin levels (greater than 80 ng/ml). In these cases the hypophyseal response to Gn-RH is frequently found (61%) to be negative and, moreover, the ovarian response to administered gonadotropins seems to be diminished. Increasing HPRL levels often appear to be associated with a negative response to the other above-mentioned tests.