In this paper, the relationship between schizophrenia, suicide and serotonin will be examined. Throughout, it will be argued that the fundamental problem does not lie with the neurotransmitter per se, but rather with uncontrolled fluctuations of brain glycaemic levels acting in conjunction with insulin resistance. It will be shown that the area of dopaminergic and serotonergic activity in the brain is intimately tied to the relative distribution of the central glucose transporters and, hence, to glucose metabolism and insulin activity. It will be argued that mania and positive schizophrenia represent a continuum of liability associated with hyperglycaemia, hyperdopaminergia, and hyperserotonergia. In contrast, depression and negative schizophrenia represent another continuum of liability involving hypoglycaemia, hypodopaminergia, and hyposerotonergia. This serves as a useful distinction in drawing together a large number of seemingly unrelated, diverse facts concerning both schizophrenia and suicide and, in particular, the possible relationship that obtains between cholesterol-lowering drugs, low serotonin and suicide. Essentially, this paper reaffirms a previously stated contention that mental illness, in its many guises, is a general manifestation of a diabetic brain state which has been termed 'cerebral diabetes'.