Abstract Brain metabolic abnormalities and aberrant dopamine (DA) metabolism have been reported in patients with schizophrenia. The authors hypothesized that mitochondria is a primary target of damage by increased free radical generation secondary to increased DA metabolism by monoamine oxidase (MAO). Epstein–Barr virus (EBV)-transformed human B lymphocytes cell lines derived from patients with schizophrenia and normal controls were incubated in the absence or presence of DA, hydrogen peroxide (H 2O 2), or rotenone (Rot). The cells were then stained with rhodamine 123 (Rh 123) and analyzed for uptake using flow cytometry. Compared with untreated cells, DA significantly decreased Rh 123 uptake by the mitochondria. This effect was similar to the control cells treated with H 2O 2 or Rot. Nevertheless, there were no differences in Rh 123 uptake between the cells of schizophrenic patients and normal controls. This study shows that DA can impair the mitochondria membrane potential but that mechanism may not be evident in schizophrenia.