Plasma carotenoid responses were determined in 36 healthy men and women before and after being fed controlled diets with a moderate amount of fat (26% of total energy) and a high carotenoid content (approximately 16 mg/d) for two 15-d periods. In addition, broccoli (205 g/d) was provided either during the first or the second 15-d residency period in a crossover design. Plasma was digested with lipase and cholesterol esterase, and carotenoids were extracted and measured by using HPLC. Three oxygenated carotenoids (lutein, zeaxanthin, and cryptoxanthin), three hydro-carbon carotenoids (alpha-carotene, all-trans-beta-carotene, and 13-cis-beta-carotene), and four geometric isomers of lycopene (15-cis-, 13-cis-, 9-cis-, and all-trans-lycopene) were separated by using a C30 carotenoid column. A small unidentified peak coeluted with standard 9-cis-beta-carotene and was identified as zeta-carotene (lambda(max) = 400 nm). The concentrations of plasma lutein, cryptoxanthin, alpha-carotene, 13-cis-beta-carotene, all-trans-beta-carotene, and cis- and trans-lycopenes were all significantly increased (P < 0.05) on days 6-16 by the high-fruit and -vegetable diets. The provision of additional broccoli for 5 d to the basic high-carotenoid diet resulted in a further significant increase in the serum concentration of lutein compared with the feeding of the basic high-carotenoid diet alone. Most of the measurable carotenoids of human plasma can be increased by moderate alterations in diet within a short time, although the magnitude of the plasma response may be related to the baseline carotenoid concentrations.