Autoantibodies reactive with denatured histones and with epitopes requiring the native histone-DNA structure in chromatin have been measured by many techniques. The presence of antichromatin antibodies is useful in diagnosing SLE and in diagnosing lupus induced by procainamide and certain other drugs such as quinidine, isoniazid, sulfasalazine and acebutolol (93). Appropriate antibodies have been reported in about 50% of patients with SLE and about 75% of patients with drug-induced lupus (29, 80). Especially, antibodies against histone-DNA complexes seem to be of some diagnostic value (94).