Fourteen synthetic steroids and androstenedione were examined in ovariectomized ewes for oestrogenic activity when administered alone and with oestradiol benzoate by intramuscular injection. None of the compounds investigated was active when administered alone, as assessed by the vaginal smear assay, and only androstenedione produced a behavioural response. Androstenedione had a MED of 8·8 mg. but was less active when administered intravenously. Several steroids acted as anti-oestrogens when injected with oestradiol benzoate. Eight steroids inhibited the behavioural response and four the vaginal response. An additive response was found with androstenedione for behavioural response and with 17β-ethyl-17-hydroxy-19-nor-4-androsten-3-one (SC-5914) for vaginal response.
Vaginal and behavioural responses were not necessarily related, and responses obtained in the ewe to particular steroids were not identical with those obtained in laboratory animals by other workers using similar tests.