19-nortestosterone (nandrolone) or its decanoate was tested in six animal models for autoimmune disease. The compound was found capable of inhibiting the development of disease symptoms or the deterioration of certain immune parameters in three out of five models of spontaneous autoimmune disease: NZB/NZW F1 (NZB/W) mice (lupus glomerulonephritis, Sjögren's disease-like syndrome), NZB (lupus glomerulonephritis, autoimmune haemolytic anaemia) and OS chickens (thyroiditis). No effect of the compound was seen in MRL lpr/lpr mice (lupus glomerulonephritis, lymphoproliferative disease) and in BB rats (insulin-dependent diabetes mellitus; IDDM). Nandrolone decanoate also seems to be active in myasthenia gravis evoked in rats immunised with acetylcholine receptor but further experiments are necessary to confirm this. In a first experiment also ethylestrenol was found to give favourable effects in the model.