Samples of the nondialyzed platelets of l4 pairs of monozygotic twins discordant for schizophrenia were assayed for their ability to enzymatically form the hallucinogen dimethyltryptamine. The schizophrenic twins had higher mean levels of enzyme activity than their non-schizophrenic co-twins, whose mean level of enzyme activity was equal to that of 22 normal subjects. This finding suggests that the higher levels of enzyme activity found in schizophrenics is produced by their environment and is not genetically determined.Abstract Teaser