The Lys198Asn polymorphism of the endothelin-1 gene has been associated with increased blood pressure levels in several studies involving European and Australian adults. The purpose of the present study was to examine the potential moderating influence of ethnicity, obesity, and socioeconomic status on associations between the ET-1/Lys 198Asn polymorphism and hemodynamic function at rest and during two laboratory stressors (video game, forehead cold) in a sample of 161 black and 213 white American normotensive young adults (mean age, 18.5 ± 2.7 years). Carrier status of the T allele was not associated with resting blood pressure or total peripheral resistance index. However, carriers of the T allele showed greater diastolic blood pressure increases to the video game (P<0.04), particularly among those who were obese (P<0.02). Carrier status also interacted with socioeconomic status such that T allele carriers who came from lower socioeconomic status backgrounds exhibited the greatest increases in systolic blood pressure to the video game challenge (P<0.05). In conclusion, the findings point out the importance of examining the impact of genetic polymorphisms on blood pressure control phenotypes within the context of potentiating environmental factors.