Human skin fibroblasts of about the same population doubling level, derived from donors of different age, were cloned. After 14 days of growth, the clones were morphologically classified, and cell counts were performed. Significant differences between the three age groups (infant, young adult, old adult) examined concerned the percentual clone type distribution. The size of a single clone depended on the clone type referring to the differentiation level of the cells in all age groups.