The accumulation of β-carotene in serum and skin was evaluated in human volunteers. A single 51-mg dose of β-carotene given in the absence of dietary fat resulted in no detectable change in serum β-carotene. The same dose administered with 200 g fat increased serum β-carotene 2.5-fold at 40 h. Similarly, administering β-carotene daily in three divided doses with meals raised the serum β-carotene concentration three times as high compared with the same total dose administered once a day; both regimens had the same time constant for serum accumulation: 9–10 d. Remittance measurements of skin color demonstrated that the accumulation of β-carotene in skin was delayed by up to 2 wk compared with serum accumulation. These data indicate that β-carotene absorption requires dietary fat and is enhanced by administering with meals but there is a long time constant for serum (10 d) and tissue (several weeks) accumulation.