Most human cancers arise in epithelial tissues, which are critically dependent on vitamin A for normal differentiation and proliferation. Dietary carotenoids consist of individual retinoids--pro-vitamin A precursors and non-pro-vitamin A precursors-displaying different biological activity. Although epidemiological data suggest that low serum vitamin A levels were associated with an increased risk of cancer, it is not known whether one specific or all vitamin A carotenoids are involved. To assess whether the plasma carotenoids are related to the nutritional or cancer-bearing state, a study was conducted to measure total and individual carotenoids in four groups: cancer-bearing, malnourished; cancer-bearing, well-nourished; non-cancer, malnourished; and well-nourished volunteers of comparable age and sex. There was no difference in total carotenoids and pro-vitamin A precursors between the well-nourished--both normal volunteers and cancer patients. Malnourished cancer and non-cancer patients had significantly (p less than 0.05) lower value of both. Most of the circulating carotenoids in all groups were the non-pro-vitamin A precursors. Both malnourished cancer and non-cancer patients had lower values than well-nourished (p less than 0.05). Differences were related to nutritional state, rather than presence of cancer.