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352 rats were used to study the effects of graded levels of lactogenic hormone (LGH) alone and in combination with PMS and HCG, on the formation of the decidual cell reaction (DCR) in intact and in hypophysectomized rats. Maximal DCR occurred in intact rats and in hypophysectomized rats treated with LGH + HCG and with LGH + HCG + PMS. A marked but significant smaller DCR was found in hypophysectomized rats treated with PMS + LGH. The DCR was absent or very minute in hypophysectomized, LGH-, PMS- or HCG-treated rats. The results indicate, that LGH alone is not capable of inducing a DCR. The addition of ICSH to LGH results in an adequate condition for the production of the DCR by uterine trauma.

For LTH-determination in biological material without preliminary extraction procedures the pigeon crop sac assay, performed by the micro-method of Grosvenor & Turner(1958), and modified by the addition of prednisolone to the standard or test material was used. Serum samples of lactating women caused no inflammations of the skin of the pigeons, and the crop sacs hardly showed any signs of inflammation. Reaction sites could be measured more easily, and the LTH activities in the plasma were about 3 times higher than in plasma processed by the acetone extraction method of Sulman(1956).