The effects of individual and multiple antioxidant vitamins on growth and morphology of human nontumorigenic (2HPC8) and tumorigenic (2HP1G) parotid acinar cells in culture have not been investigated. Our study showed that tumorigenic acinar cells were more sensitive than nontumorigenic acinar cells to individual vitamins such as vitamin C, beta-carotene (BC), d-alpha-tocopheryl succinate (alpha-TS), and retinoic acid (RA) and a mixture of four vitamins (vitamin C, BC, alpha-TS, and RA). The effect of individual vitamins on tumorigenic acinar cells depended on the dose and the type of vitamins. Vitamin C at a low concentration stimulated growth, but at a high concentration it inhibited growth. BC was most effective in reducing growth, and it alone caused extensive morphological changes in tumorigenic acinar cells. A mixture of four vitamins at appropriate doses was more effective than a mixture of two or three vitamins at the same doses in reducing the growth of tumorigenic acinar cells. The extent of growth inhibition depended on the dose and the type of vitamins. Our results suggest that the use of multiple antioxidant vitamins is essential for a maximal reduction in cancer incidence among a high-risk population. The use of one or two vitamins may be ineffective or even harmful.