Abstract
SUMMARY: Maximum sensitivity to oestradiol-3:17 β and dimethylstilboestrol (DMS) in interrupting pregnancy or inhibiting deciduoma formation occurred approximately 72 hr. after mating. Administration of the two compounds together resulted only in additive action and not antagonism. The inhibitory action of DMS in these experiments may have been due to its pro-oestrogenic rather than to its anti-oestrogenic activity, but this is by no means certain.