The water content of the skin is greatly influenced by ground substances, which may be responsible for wrinkling and laxity of the skin accompanying the cutaneous aging. Therefore, water content in the skin is presumed to be a critical determinant in cutaneous aging. This study was aimed at clarifying the change in water content and the content of glycosaminoglycans (GAG) of rat skin in relation to aging. Sprague-Dawley rats were divided into 6 groups: 1-, 3-, 6-, 12-, 18- and 24-month-old groups. Two-to-three grams of skin tissue samples were taken from the back, and a half of sample was dried at 160 degrees C for 30 min with electronic moisture balance, and water content was assessed as decreased weight by heating. To measure change of GAG of the rat skin, another half of samples were extracted with 0.1 M sodium phosphate buffer (pH 7.4 NaPB) and 2 M guanidine-HCl/Tris buffer (pH 7.4). The resultant insoluble pellet was dried at 50 degrees C in a drying over for 72 h after two washings and the dry weight was recorded. The amount of sulfated GAG in the skin extracts was measured by alcian blue precipitation assay, and the amount of uronic acid (UA) was assayed in the skin tissue extracts and the dried skin using the carbazole reaction. The water content of the rat skin decreased with age, and a similar decreasing pattern in the amount of sulfated GAG and UA of the rat skin tissue was observed with aging. One hundred times of UA was obtained in dry rat skin tissue, as compared with that of the skin extracts. In conclusion, there occurs a significant decrease of water content in the aged rat skin, which may be related to the change of GAG with intrinsic aging of the skin.