A and C57BL/6 inbred mice were used as models for investigating interactions between aging processes and the genes that regulate the immune system, the major histocompatibility complex (MHC, H-2) genes. The C57BL/6 (H-2[superscript] b) mice exhibited significantly longer mean lifespans than the A (H-2[superscript] a) mice, as has been observed by other investigators. Backcross and F[subscript] 2 generation offspring from the parental A and C57BL/6 mice were tested for dependence of longevity upon H-2 type. The effects of H-2 type upon lifespan were statistically significant only for the oldest surviving (i.e., "10[superscript] th decile") mice, in agreement with observations made by other investigators using other mouse strains. In contrast with the relatively limited H-2 effect, analyses of the interaction between gender and lifespan in these mice showed that females generally lived longer than males;When the H-2 genes of the A and C57BL/6 mice were tested at the molecular level, the per cell expression of H-2 class I mRNA tended to increase from 2 months (young) through 29 months (old) aged mice. No statistically significant difference in H-2 class I mRNA expression was detected between the genders or between the strains;Preliminary studies of H-2 class I mRNA expression from the early stages of life (i.e., in preimplantation CF1 mouse embryos) indicated that H-2 mRNA rises rapidly from the oocyte to blastocyst stage of development. However, final conclusions concerning this observation should be reserved until the experiments have been adequately repeated;Finally, in addition to the results discussed in the body of this dissertation, my research on aging and the MHC contributed to several publications which are summarized in the Appendices. Included are studies of the immune system of allophenic mice and the evaluation of glucose phosphate isomerase as a marker for studying mouse lymphocytes.