Previous studies have indicated that plasma levels of retinol are decreased in some cancer patients and that lower levels of retinol could be associated with a poor response to chemotherapy. This pilot study was conducted to determine whether it is possible to increase plasma levels of retinol in cancer patients by supplementation with retinol. Plasma levels of retinol were measured by high-performance liquid chromatography in 46 patients treated with chemotherapy for various malignancies and in 43 control individuals; cancer patients were supplemented orally either with 25,000 or 50,000 IU of retinol daily during up to 3 months. Initial levels of retinol were lower in cancer patients than in the control group; the decrease was significant in women with liver metastases but not in men. Women supplemented with 25,000 IU had a significant increase of their retinol levels after 1 month but this effect was not maintained during continued supplementation; in women receiving 50,000 IU daily, a sustained increase in retinol level was maintained during the 3 months of supplementation. In men, a similar trend was produced by the supplementation but the increases were not significant. Retinol levels decreased to initial levels within 1 month of discontinuation of supplementation, indicating the need for continuous supplementation.