Corneal keratocytes are often confounded with fibroblasts, although their matrix-synthetic phenotype is quite different as shown by the nature and relative amount of the different collagens and proteoglycans-glycosaminoglycans synthesized. In these experiments, we compared the concentration of collagens excreted in the culture medium by human corneal keratocytes and skin fibroblasts at three consecutives passages. Although the keratocytes excreted less collagen at earlier passages, they approached and reached fibroblasts at later passages. This can be taken as an indication of the progressive loss of a specific keratocyte phenotype with increasing passages (in vitro aging). The effect of rhamnose-rich oligo- and polysaccharides on collagen secretion also confirmed the subtle differences between these two cell-types, as well as the difference between saturation density of both cell types at confluence and the proportion of dead cells floating on top of the culture medium. These differences were also attenuated with passage number without disappearing completely. The significance of these findings will be discussed in the light of previous results in our and other laboratories on matrix-secreting phenotypes and aging.