Estrogens appear to play a central role in the immune response and immune-mediated diseases. Recent studies have shown the presence of estrogen receptors on the cells involved in the immune response, namely thymocytes, macrophages and endothelial cells. Particular attention has been focused on the dose-dependent influence of estrogen on the immune response, which appears to be related to the clinical symptoms of autoimmunity (i.e. the effects of pregnancy or oral contraceptive pills). The influence of estrogens on cytokine production by target cells, through interference with their transcriptional activity, has also been the focus of various studies. The effect of estrogens on the expression of the protooncogenes and oncosuppressor genes involved in programmed cell death (apoptosis) might also be relevant to human autoimmunity, in particular the uncontrolled synovial lining cell hyperplasia associated with rheumatoid arthritis and the prolonged T-cell survival in systemic lupus erythematosus. Estrogen-induced immunomodulation is a subject of growing interest and stimulating research.