Although personality is thought to be 50% heritable, consensus has not been reached about the specific genes involved, interest in genes affecting personality and behavior continues because of the linkage of personality traits with both physical and mental illness. One hundred and twenty years of study of the ABO blood types and the genes causing them has led to more precise assignment of genotype-phenotype linkage. Countries like Japan and Korea with 100 years history of study of ABO blood groups and personality as well as other countries have published research with no consensus. Introversion is a well-studied personality trait with 50% genetic causation. Dopamine system has been linked to the introversion-extroversion spectrum with high dopamine linked to introversion. Dopamine beta hydroxylase determines the ratio of dopamine to norepinephrine. Dopamine beta hydroxylase gene, DBH, is in linkage disequilibrium with ABO gene thus offering insight into the ABO findings related to personality traits. ABO blood groups have been studied with some but not all studies finding type AB associated with introversion. One explanation for the inconsistent replication of findings could be that genotypes would show more differences than phenotypes. ABO A allele, ABO B allele or the synergism of both alleles could be the driver of introversion trait in ABO AB. Patients in an obstetric gynecology practice appeared to demonstrate a tendancy to introversion in phenotype ABO B. Since we had access to ABO blood phenotypes instead of genotypes of our obstetric gynecology office patients, we hypothesized that phenotype ABO AB when compared with ABO O would be associated with higher introversion since these phenotypes were also genotypes and since ABO O unlike ABO AB is not found associated with introversion in extant research. Though ABO B allele was observed to be the likely cause of introversion in patients and since we had available only phenotypes of ABO to use in search of genetic allele that causes introversion trait, ABO AB needs to be dissected to see whether ABO A allele or ABO B allele is the driver of the introspective trait. Based on the literature and on observation, the hypothesis was that ABO B is the driver of introversion trait. A pilot student of 225 obstetric gynecology patients using the online NPA personality test showed higher scores for introversion tendancies in ABO AB compared to ABO O and when ABO AB was compared to ABO A. This supports ABO B as the driver of introversion tendancies in the ABO gene. Studies using ABO genotypes instead of ABO phenotypes should provide further support for this hypothesis. Given the support for introversion tendancies in personality caused by higher dopamine genetically with dopamine beta hydroxylase low activity and this dopamine state being common mechanism for such conditions as schizophrenia and autism, continued discoveries of genes that impact this state will lead to many health implications.