Abstract
SUMMARY 1. An assay method for urinary FSH depending on an increase of ovarian weight in mice treated with HCG has been examined experimentally. 2. Synergism was not observed when mixtures were assayed by this method. However, when 'total gonadotrophic activity' was estimated by the weight increase of the mouse uterus there appeared to be some evidence of synergism. 3. The administration of prolactin in total dosages up to 10 i.u./mouse did not interfere with the assay. 4. The addition of oestrogens sometimes affected the assay results and frequently caused a departure from parallelism.