Although in vitro models are often used in beta-carotene research, knowledge about the uptake and metabolism of beta-carotene in cell lines is lacking. We measured by HPLC the intracellular levels of beta-carotene and its metabolites in 9 human intestinal and lung cell lines after exposure to 1 microM beta-carotene during 2, 6, 30, 54 h, and 3 weeks. In three colorectal carcinoma cell lines only low levels of beta-carotene could be detected and an apparent linear increase in intracellular beta-carotene was observed during the whole exposure period of 3 weeks. The remaining cell lines (an SV40 transformed colon cell line, a small intestinal carcinoma cell line and several lung cell lines) had medium or high intracellular beta-carotene levels. In these cell lines intracellular beta-carotene quickly increased during the first 54 h of exposure and after 3 weeks no further increase was observed, suggesting a stable level of beta-carotene after 54 h. Estimated intracellular concentrations at steady-state levels varied between 2 and 5 microM (low) or 9 and 55 microM (medium/high). Our results seem to indicate that an active uptake mechanism of beta-carotene exists in at least a subset of cell lines. Seven different beta-carotene metabolites were detected in the various cell lines (cis-carotene, retinol, three epoxy-carotenes, and two retinyl esters). Metabolite levels were the highest in cells with medium or high beta-carotene levels. Each cell line appeared to have a distinct metabolite profile. No intestinal or lung specific pattern could be found, but two epoxy-carotene metabolites were not detectable in the colon cell lines.