OBJECTIVE Previous research has demonstrated that a theoretical model including measures of life stressors, social support, and coping style significantly predicts psychological distress. This study tested plasma pyridoxine (vitamin B6) deficiency status as a predictor of overall psychological distress and specific mood states in this model, controlling for HIV-1 serostatus. METHOD Subjects included HIV-1+ (N = 76) and HIV-1- (N = 58) recently bereaved homosexual men. At baseline, subjects completed a battery of psychosocial questionnaires, together with a physical examination and venipuncture. The Profile of Mood States (POMS) provided measures of overall psychological distress as well as specific mood states. Pyridoxine deficiency status (a categorical measure of deficient vs. adequate status) was determined with a bioassay of erythrocyte aspartate aminotransferase activity. RESULTS Pyridoxine deficiency was a significant predictor of increased overall psychological distress in this model, controlling for life stressors, social support, coping style, and HIV-1 serostatus. In post hoc analyses of specific mood state effects, pyridoxine deficiency status was significantly associated with increases in depressed, fatigued, and confused mood levels, but not with those of anxiety, anger, or vigor. DISCUSSION These findings suggest that adequate pyridoxine status may be necessary to avert psychological distress in the setting of bereavement. Inasmuch as pyridoxine is a cofactor for 5-hydroxytryptophan decarboxylase--an enzyme in the biosynthesis pathway of serotonin--serotonin level in the brain is implicated as the mediating factor.