The present study was focused on the effects of feeding to young (2 mo. old) and aged (30 mo. old) rats either a folate repleted or a folate deficient diet for seven weeks on several markers of folate metabolism. Serum and liver folate contents were determined, and hepatic distribution of folates based on glutamic acid chain length and pteridine ring was obtained. In addition, liver s-adenosylmethionine (Ado Met) and s-adenosylhomocysteine (AdoHcy) concentrations, as well as serum homocysteine concentration have been also determined. Ageing itself seems not to be associated with lower hepatic folate content, but in serum a 50% decrease was observed. Feeding the folate deficient diet did result in significant lower (p < 0.001) liver folate content in both age groups, and in marked decreases in serum folates. These quantitative changes in the folate deficient groups were associated with an elongation of the glutamate chain length, mostly represented by a significant decrease in the proportion of pentaglutamyl derivatives, an increase of hexaglutamyl, and appearance of hepta and octaglutamyl folate derivatives. However, there were no important modifications in the pteridine ring distribution regardless of the age and level of dietary folate. In the present study, ageing seems to be associated with a significantly lower AdoMet/AdoHc ratio (65% decrease, p < 0.05), irrespective of the folic acid included in the diet.(ABSTRACT TRUNCATED AT 250 WORDS)