It is well known that soon after his youthful creative years (1664–1666) Newton developed an interest in alchemy, and he performed his first documented experiment in 1678 (2). He handled many heavy metals, including mercury, meticulously recording their properties and, in particular, their taste. Of the 108 entries on taste, a typical one (3) reads, "strong, sourish, ungrateful," referring to mercury. Besides mercury, there is evidence in Newton’s journals of exposure to lead, arsenic, and gold—all of which can cause psychiatric symptoms. On the basis of arguments presented by Christianson (4), Jeste et al. argued against mercury poisoning as a possible cause of Newton’s illness, since symptoms such as tremor and gum ulceration seem to be absent. However, we have no documentary evidence that these symptoms were indeed absent. Moreover, it is known that mercury and other heavy metal poisoning can present a constellation of symptoms, with no specific symptoms being diagnostic for poisoning (5), which further weakens the argument. At any rate, one cannot ignore the fact that Newton not only was exposed to mercury but actually ingested it by his own account.