The effects of aging and acupuncture on brain MT1 and MT3 mRNA levels in senescence-accelerated mice (SAMP10) and accelerated senescence resistant mice (SAMR1) were analyzed by Northern blot analysis. Both MT1 and MT3 mRNA levels in SAMR1 were increased significantly from birth to month 4 and decreased gradually thereafter. In SAMP10, the MT3 mRNA level followed the same pattern as in SAMR1 before month 4, then decreased from month 4 to 6, but was over-expressed and exceeded the previous level at month 8. The MT1 mRNA expression in SAMP10 showed a zigzag pattern. Of two groups of SAMP10 mice treated with acupuncture, the Xingnao group (PC6 and Du26 as acupoints) and the Zibuganshen group (BL18 and BL23 as acupoints), both showed a higher MT1 mRNA level and a lower MT3 mRNA level than the age-matched control group. Meanwhile, in both of the acupuncture groups, the ratios of MT3 to MT1 were down-regulated to the normal range. Overall, these results suggested that over-expression of MT3 mRNA and the increase in MT3 to MT1 ratios in SAMP10 were correlated with aging, and could be an important physiological and pathological event in the aging process. Acupuncture altered the expression levels of MT1 and MT3 mRNA and differences between the effects of the two stimulated acupoints were seen. Therefore, maintenance of the balance between MTs mRNA expression and correct MTs concentrations is crucial for brain-endocrine-immune response and normal aging. Acupuncture could improve zinc ion bioavailability, by maintaining the balance between MT1 and MT3 mRNA expression levels and might explain one of the mechanisms by which acupuncture treatments defer aging and treat some age-related neurodegenerative diseases.