Impaired lymphocyte and granulocyte function in the aged may, in part, reflect intrinsic aged-related biochemical alterations. In this study we compared the ribonucleotide contents of lymphocytes and granulocytes from young and old subjects evaluated by means of an HPLC-anion exchange method. We found that in general both populations from old subjects present higher levels of the various nucleotides, in particular: ATP, UDP, CTP, UDP-glucose in granulocytes, AMP, CTP, UDP-N-acetylglucosamine, UDP-glucose in lymphocytes. These data suggest that these molecules accumulate in aged subjects because of altered biochemical pathways. The increased pool of UDP-sugars, in particular, could be due to a depressed activity of some glycosyltransferases which therefore fail to glycosylate some plasma membrane cell proteins, thus accounting for their functional impairment.