Objective: The authors measured N-acetylaspartate (a putative neuronal marker), using in vivo proton magnetic resonance spectroscopic imaging (1H- MRSI), in the frontal lobes of schizophrenic patients and normal subjects. Method: Frontal lobe 1H-MRSI was performed bilaterally on 24 medicated schizophrenic patients and 15 healthy comparison subjects. Levels of N- acetylaspartate, creatine, and choline were determined. Results: Relative to the comparison group, the patients with schizophrenia demonstrated significantly lower levels of N-acetylaspartate in the left frontal lobe. There was no association between level of N-acetylaspartate and duration of illness or medication dosage. No differences between groups or lateralized asymmetries in choline or creatine were noted. Conclusions: This preliminary study provides support for decreased N-acetylaspartate in the left frontal lobe in schizophrenia and neuronal dysfunction in this brain region.