To the Editor: We thank Drs. Spivak and Epstein for their letter. They propose that Newton’s psychosis reflected the effects of metal poisoning. Several biographers of Newton considered but rejected this possibility because it was not supported by available evidence (Christianson, 1984; 1). Tremor is a frequent symptom of such poisoning, yet none was apparent in any of Newton’s handwritten documents from that period (1). Another frequent symptom of mercury poisoning is a loosening of the teeth. However, as Christianson (1984) noted, "Newton died, at the age of eighty-four, with all of his secondary teeth but one, rather remarkable for a man of his day" (p. 359). None of the documents from Newton (or the observations by his acquaintances) mention any of the physical symptoms frequently associated with metal poisoning, such as uremia, jaundice, emaciation, darkened nails, premature aging, weight loss, lethargy, visual disturbances, convulsions, coma, or paralysis (1).