Sixty schizophrenic outpatients with prominent, primary negative symptoms are treated with antipsychotic medication and are randomly assigned to D-cycloserine or placebo for a 6-month, fixed-dose trial. The primary outcome measure is the total score on the Scale for Assessment of Negative Symptoms (SANS). A neuropsychological battery, which emphasizes tests sensitive to prefrontal cortical function, is administered. Blood is obtained at several time points and CSF is obtained at Week 8 for assay of concentrations of D-cycloserine, glutamate, HVA, and 5HIAA.