The aim of this study was to evaluate the peripheral representation and the clonogenic capacity of CD34(+) progenitor cells from 130 healthy subjects (80 females and 50 males) ranging in age from 16 to 100 years. We demonstrated that the absolute number of circulating CD34(+) cells progressively and significantly decreased with advancing age, with a 2-fold reduction in subjects aged more than 80 years. The number of granulocyte-macrophagic (CFU-GM), erytroid (BFU-E), and mixed (CFU-GEMM) colonies which developed from the number of CD34(+) purified cells per ml, progressively and significantly decreased with advancing age. The reduction of both CD34(+) cell number and clonogenic capacity during aging was statistically significant in males but not in females. When evaluated on a per cell bases, a significant age-related decrease in the number of CFU-GM colonies was observed in female but not in male subjects. Our study demonstrates the influence of gender on age-related alterations of the number and clonogenic capacity of CD34(+) cells in the peripheral blood. This evidence deserves particular consideration for the future planning of stem cell therapy in age-associated debilitating diseases.