Luteinizing hormone (LH) concentration was measured in the jugular plasma of six groups of ovariectomized ewes which were fed oestrogenic clover (Trifolium subterranean L. Gray cv. Yarloop) for 3 days. Ewes in groups B, D and F received an injection of oestradiol-17beta (E2) 24 h after first being offered clover, whilst ewes in groups A, C and E received no oestrogen treatment. Following the initial ingestion of clover, plasma LH concentrations for all groups fell within 3 h and then increased significantly. Each subsequent feeding of clover usually resulted in a temporary decrease and then an elevation of the LH concentrations. When ewes in groups B, D and F were injected with E2, LH concentrations fell and remained low for approximately 9 h, then increased to a peak of 72-3 +/- 10-4 ng/ml within 5 h. The LH concentrations remained elevated for a period of about 12 h. The present paper indicates that the ingestion of oestrogenic clover by ovariectomized ewes results in a depression and then a release of LH, and that this release does not appear to deplete the pituitary of LH or cause refractoriness to an oestrogenic stimulus.