To the Editor.— Several conclusions in the article by Mayer and Williams, which appeared in the July issue of the Archives (31:24-26, 1974), appear to us to be misleading. They state that such incrementing responses are most likely with weakness in the upper extremities (? not necessarily in the muscle they tested) and during phase of the disease or during steroid therapy. In our material ( Ann NY Acad Sci 183:287-302, 1971) incrementing responses, though often recorded from strong and weak muscles, were most marked in normal or only slightly weak muscles. None of our patients were receiving steroids or appeared to be in a particularly progressive phase of the disease, and we agree with Simpson (Myasthenia Gravis and Myasthenic Syndrome, in Walton JN (ed): Disorders of Voluntary Muscle . London, J & A Churchill Ltd, 1969) that incrementing responses tend to occur in strong muscles—a point that is easily confirmed