['Inflammation is known to affect sulfur amino acid metabolism. Aging is associated with an increased prevalence of inflammatory conditions, but the metabolism of methionine has been poorly explored in the elderly.', 'The aims of this study were to compare methionine kinetics between elderly and young subjects and to explore the effect of aging on the response to a mild inflammatory challenge induced by a vaccination.', 'Seven elderly volunteers aged 66-76 y and 8 young volunteers aged 22-26 y were studied before and 2 d after a vaccination (diphtheria, tetanus, poliomyelitis, and typhoid vaccines). Methionine kinetics were measured by using an infusion of L-[1-13C, methyl-2H3]methionine in the postabsorptive and fed states.', 'Before vaccination, the contribution of homocysteine remethylation to methionine-methyl flux (Qm) and the ratio of remethylation to homocysteine transsulfuration were significantly lower in the elderly subjects than in the young subjects (P < 0.05). In contrast, the contribution of transsulfuration to methionine transmethylation was higher in the elderly (P < 0.05). Vaccination significantly increased the ratio of transsulfuration to transmethylation and decreased the ratio of remethylation to Qm (P < 0.05).'] Are methionine kinetics altered in the elderly both in the basal state and after vaccination?