Abstract Retroperitoneal fibrosis (R.P.F.) and a positive direct Coombs test developed in a patient who had received 1·4 kg. of α-methyldopa over a period of 5 years. Immunofluorescence microscopy demonstrated deposits of IgG, IgM, and IgA on the collagen fibres of the R.P.F. Biopsy specimens of the temporal artery, the right kidney, and the R.P.F. did not show signs of general arterial disease on light, immunofluorescence, and electron microscopy. Drugs which provoke autoimmunisation and interfere with nervous transmission are known to induce deposition of collagen or R.P.F. This suggests that R.P.F. in this patient was probably caused by α-methyldopa.