Ingestion of phytosterols has been shown to reduce plasma cholesterol in both animals and humans. The esterified forms of phytosterols are increasingly being incorporated into margarine and fat spreads, which are then marketed as functional foods. The aim was to assess the cytotoxicity and uptake of four phytosterols, beta-sitosterol, campesterol, stigmasterol and stigmastanol, in human intestinal cells in culture. Another aim was to determine if phytosterols would interfere with alpha-tocopherol or beta-carotene uptake by these cells. Human adenocarcinoma Caco-2 cells were supplemented for 24 h with increasing concentrations (0-12.5 microM) of each phytosterol. Cytotoxicity was assessed by neutral red uptake (NRU), lactate dehydrogenase release (LDH) and fluorescein diacetate/ethidium bromide (FDA/EtBr) assays. The phytosterols had no significant effects on Caco-2 cell viability assessed using LDH and FDA/EtBr assays. The highest concentrations of beta-sitosterol and campesterol tested (12.5 microM) resulted in decreased cell viability assessed using the NRU assay. All phytosterols were taken up by Caco-2 cells in culture. The results demonstrate a reduction in the uptake of beta-carotene when Caco-2 cells were supplemented with 20 microM beta-sitosterol. beta-Sitosterol did not interfere with alpha-tocopherol uptake by the cells. In conclusion, Caco-2 cells are a useful model system to study potential interactive effects of phytosterols with fat-soluble dietary components.