The enzyme activities which depended on the ascorbic acid (AsA) tissue levels were assayed to investigate the effect of erythorbic acid (ErA) administration on the AsA availability in the guinea pigs adminis-tered 5mg of AsA/day or 1mg of AsA/day. The guinea pigs were given 5mg of AsA and 1, 5, 20, 100mg of ErA/day, or 1mg of AsA and 1 or 20mg of ErA/day for 16 days. The animals were sacrificed, blood was collected, and their livers were removed. The activities of liver aniline hydroxylase, liver acid phosphatase, and serum alkaline phosphatase, as well as the liver cytochrome P-450 content were measured. These enzyme activities and the liver cytochrome P-450 content of animals administered 5mg of AsA seemed to show no change regardless of ErA supplement. Animals administered 1 mg of AsA showed different activities of liver aniline hydroxylase and liver acid phosphatase compared with those of animals administered 5mg of AsA; however, the enzyme activities in animals administered 20mg of ErA together with 1mg of AsA were similar to those of the animals administered only 5mg of AsA. These results indicated that ErA administration had no effect on the enzyme activities and the liver cytochrome P-450 content in the 5 mg ASA-supplemented animals, but administration of 20 mg of ErA was effective to maintain at normal levels the activities of liver aniline hydroxylase and liver acid phosphatase in the 1mg AsA-supplemented animals.