Proton-Magnetic Resonance Spectroscopy (1H-MRS) may serve as an important tool for identifying biomarkers that aid the understanding of early psychosis, as development of this condition may be associated with metabolite concentration changes that reflect an alteration in glutamatergic mechanisms. The current study explored 1H-MRS metabolite concentrations in the striatum and anterior cingulate cortex (ACC) as potential biomarkers of psychosis-risk symptom severity. In a sample of 12 adolescents at clinical high-risk for psychosis, the subclinical symptom of grandiosity significantly correlated with glutamate in the ACC. Striatal glutathione, a marker of oxidative stress linked to the glutamatergic system, significantly correlated with grandiosity. Anterior cingulate glutathione significantly correlated with grandiosity and disorganized communication. These findings suggest that within a small sample of young people at clinical high-risk, glutamatergic metabolites are correlated with symptomatology generally predictive of conversion to psychosis. These mechanisms may serve as relevant biomarkers for facilitating prediction of symptom severity and providing insight into the etiology of early psychosis. •A sample of 12 adolescents at clinical high risk for psychosis were scanned.•Grandiosity correlated with glutamate in the anterior cingulate cortex (ACC).•Grandiosity correlated with striatal and anterior cingulate glutathione.•Disorganized communication correlated with glutathione in the ACC.•Glutamatergic metabolites may be biomarkers for early illness symptom severity.