The injection of aged mice with 7-methyl-8-oxoguanosine (7m8oGuo) along with aggregated human gamma-globulin (AHGG) results in an enhanced anti-HGG antibody response. Aged mice injected with AHGG alone make only a feeble anti-HGG response. The enhanced response in aged mice was not significantly different from the response obtained in young-adult mice injected only with AHGG. However, the enhanced response obtained by injection of 7m8oGuo in young-adult mice was several orders of magnitude greater than that observed in the aged mice. Aged mice given a primary injection of AHGG alone failed to make a secondary response to AHGG given 90 days later, whereas aged mice injected with 7m8oGuo along with a primary injection of AHGG showed variable secondary antibody responses to AHGG. Two of seven mice showed high degrees of immunological memory equivalent to that seen in young-adult mice while others showed either meagre or no responses. The effect of 7m8oGuo appeared to be primarily on B cells, albeit the role of T cells cannot be ruled out.