Thin layer chromatography and laser densitometry were used to examine erythrocyte membrane phospholipid composition in 13 medication-free patients with schizophrenia or schizoaffective disorder and 11 healthy control subjects. The patient group had significantly decreased levels of phosphatidylethanolamine and a significant increase in sphingomyelin. The patient group also showed a trend toward decreased levels of phosphatidylinositol bisphosphate. Levels of phosphatidylcholine and lysophosphatidylcholine did not significantly differ between groups. There were no significant effects of age, body mass index, or gender on any of the phospholipid parameters. The observed alterations may point to abnormalities in key membrane-related functions, including signal transduction and ion transport.