We describe a simple assay for spinal fluid glutamine, in which glutaminase is used to deaminate glutamine and the liberated ammonia is then measured with phenol hypochlorite. The concentration of glutamine in spinal fluid is increased in coma of hepatic origin. Spinal fluid glutamine was increased above normal at the time of admission in 20 of 27 cases of Reye's syndrome, of which hepatic dysfunction is apparently a feature. There was no correlation between the initial concentration of glutamine in spinal fluid and the ultimate outcome in these patients.