The concentrations of vitamin A and total carotenoids were measured in serum and skin of 61 patients with acne vulgaris, atopic dermatitis, ichthyosis vulgaris or lichen planus, and compared with those in 37 healthy subjects. The mean serum concentrations of retinol and retinol-binding protein were significantly decreased in patients with acne (P less than 0.01) and slightly increased in those with ichthyosis (P less than 0.05), but were otherwise normal. Serum carotenoid levels did not differ between patients and controls. Superficial shave biopsies from both involved and uninvolved skin were examined for the presence of retinol (vitamin A1), dehydroretinol (vitamin A2) and total carotenoids. The mean retinol concentration was increased in lichen planus lesions (P less than 0.05) and decreased in both acne skin (involved and uninvolved) and in lesions of atopic dermatitis (P less than 0.05). The mean dehydroretinol concentration was markedly increased in lesions of atopic dermatitis and lichen planus (P less than 0.01). No consistent abnormalities were found in skin of patients with ichthyosis vulgaris. The mean carotenoid concentration in the patients' skin did not differ significantly from that in the controls. The reduced retinol level in the skin of acne patients is probably explained by diminished supply of vitamin A from the blood. The abnormal ratio of retinol to dehydroretinol in lesions of lichen planus and atopic dermatitis is possibly due to changes in cutaneous vitamin A metabolism associated with epidermal hyperproliferation and inflammation.