The contents of acid glycosaminoglycans (aGAG) was determined in the inner and medial layers of aortae from 13 newborns, 9 small children (1-5 years of age), and 10 older adults (7th decade of life). The total aGAG contents was expressed in mug hexuronic acid/100 mg dry weight. Newborns and older adults showed similiar contents of aGAG in their aortae (275.5 plus or minus 27.9 and 313.4 plus or minus 46.7, respectively). Small children had significantly less aGAG in their aortae (202.1 plus or minus 21.5). The aGAG material from aortae was fractionated by a microcolumn chromatographic procedure on cetylpyridinium chloride cellulose. No significant differences of the aGAG fractions were found in aortae of newborns and children. In both groups of children the percentage of hyaluronic acid was significantly increased and dermatan sulfate was significantly decreased when compared with aortae from older adults. The increased contents of acid glycosaminoglycans (aGAG) in aortae of human newborns is possibly caused by the concentrated hormonal environment (especially estrogens) to which the fetus is exposed in utero.