OBJECTIVE: Occupational stress is increasing in Western societies and the impact is significant at a personal, organisational and community level. The present study examined for the first time the efficacy of 3 months administration of two forms of high dose vitamin B complex on mood and psychological strain associated with chronic work stress. METHOD: Sixty participants completed the 3-month, double-blind, randomised, placebo-controlled trial in which personality, work demands, mood, anxiety and strain were assessed. RESULTS: After individual differences in personality and work demands were statistically controlled, the vitamin B complex treatment groups reported significantly lower personal strain and a reduction in confusion and depressed/dejected mood after 12 weeks. There were no treatment-related changes in other measures of mood and anxiety. DISCUSSION: The results of the study are consistent with two previous studies examining multivitamin supplementation and personal (non-work) feelings of strain and suggestive of significant decreases in the experience of workplace stress after 90 day supplementation of a B multivitamin. CONCLUSION: Given the direct and indirect costs of workplace stress, these findings point to the utility of a cost-effective treatment for the mood and psychological strain effects of occupational stress. These findings may have important personal health, organisational and societal outcomes given the rising cost and incidence of workplace stress.