- Background: Motor disturbances in vitamin B6-deficient animals were described. Some clinical experiments showed that vitamin B6 may ameliorate different drug-induced movement disorders, including tardive dyskinesia (TD). The aim of this study was to compare plasma pyridoxal-5-phosphate (PLP) levels in schizophrenic patients with and without TD. Method: This study was conducted in the Be'er Sheva Mental Health Center from February 2006 to August 2006. Eighty-nine schizophrenic inpatients (40 have TD, 22 men and 18 women, 20-66 yrs old [mean, 48 yrs] and 49 schizophrenic inpatients, 30 men and 19 women, 21-66 yrs old (mean, 49 yrs), without any symptoms of motor disturbances [the control group]) were enrolled in the study. Measurement of PLP is performed by high-performance liquid chromatography separation in all patients. Results: There was a significant difference in plasma PLP levels between patients with TD and those without TD. The discrepancy between the groups was almost entirely attributable to the PLP levels of male patients: 12.4 ± 11.4 vs 29.0 ± 12.9 nM in men (P < 0.001), and 19.7 ± 14.8 vs 22.0 ± 13.6 nM in women (P > 0.5). Conclusions: Our results suggest that schizophrenic and schizoaffective male patients with TD have lower PLP plasma levels than non-TD patients.