The immunological side-effects under treatment with antihypertensive drugs are mainly limited to autoimmunity and autoimmune disease caused by alpha-methyldopa and hydralazine. Autoimmune hemolytic anemia is more common during treatment with alpha-methyldopa. Hydralazine may induce antinuclear antibodies. Some patients develop a SLE-like syndrome. Its clinical picture is less severe and its prognosis is more favourable than that of spontaneous SLE. During treatment with low doses the disease develops exclusively in patients who are slow acetylators. It may appear also in rapid acetylators during the high dose treatment. The symptoms are usually reversible after withdrawal of the drug.