Identity and intensity of parasitism have been shown to be correlated to the host genotype at the major histocompatibility complex (MHC), a genomic region involved in the adaptive immune response. However, the evolutionary mechanisms by which parasites exert a selective force on host immune systems are unknown. This thesis investigates the relationship between parasitism and MHC genotype in two bear populations in Southcentral Alaska. We diagnosed infection using the polymerase chain reaction (PCR), targeting the ribosomal subunit of 18S of common blood parasites. Parasitism was detected in half of brown bears and 75% of black bears. We detected Eimeria spp. and several species of apicomplexan and nematode parasites, and we report here the first finding of Trypanosoma cruzi in Alaskan bears. We found no association between MHC genotype and identity or intensity of infection, suggesting that other loci or even non-genetic factors are important covariates in predicting infection status.