Reye syndrome, a reversible metabolic encephalopathy and hepatopathy, offers a unique opportunity to investigate the pharmacologic mechanisms by which a toxic-metabolic insult to mitochondria is translated into neurochemical and neurologic dysfunction. Similarity of some clinical and metabolic abnormalities between certain inborn errors of organic acid, ammonia, and carbohydrate metabolism and Reye syndrome suggests a common pathophysiologic mechanism at some level. The primary metabolic aberration in Reye syndrome is unknown. Viral, drug, and toxic precipitants in a conductive host alter glial and neuronal function, possibly by direct toxic effects or by altered transmitter metabolism and signal transduction. These events translate into a rather stereotyped progression of the clinical syndrome. Increased ICP, which is a life-threatening epiphenomenon, is the focus of conventional therapy. Investigational treatments, still in preliminary stages, are aimed at early correction of instigating metabolic abnormalities or correction of their consequences on central neurotransmission. Our fragmentary knowledge of neurotransmitter abnormalities in this disorder, which have suggested disparate interpretations, does not allow a cohesive pharmacologic theory of Reye syndrome. The greatest difficulties in interpretation of possible central mechanisms from existing data, which derive largely from peripheral tissues, is in the differentiation of primary from compensatory changes. The unitarian notion that a single pharmacologic disturbance is the source of the encephalopathy is perhaps too simplistic. It is hoped that future studies of disorders such as Reye syndrome will elucidate the intricate relationships between biochemical pathways and neurotransmitter metabolism.