A 10% or more nocturnal decline in blood pressure (BP) (dipping) is less frequent among African- (AA) than European-Americans (EA). AA also have higher rates of hypertension, cardiovascular disease, stroke and end-stage renal disease than EA and it has been suggested that differences in dipping contribute to the morbidity difference. Few studies have examined whether stress hormones (epinephrine, norepinephrine, cortisol) contribute to the ethnic difference in dipping. There is also little information regarding whether variation in proinflammatory cytokines (such as Il-6) are involved. This dissertation evaluated AA and EA differences in dipping, examining the relationships between BP and stress hormone variation and the link between stress hormones and IL-6. The reproducibility of the ethnic difference in dipping was also assessed. Ambulatory BP and self-reported diary data were collected over the course of three workdays in 51 AA and 110 EA women employed at three medical centers in New York City. Timed urine samples were also collected at work, home and during sleep from which stress hormone excretion rates and IL-6 levels were determined. Repeated measures ANOVA and ANCOVA were used to evaluate the AA-EA differences. Results show that the work-sleep decline in epinephrine predicted the work-sleep decline in BP. However, among AA, the association was much more direct. More than 95% of the dipping differences of EA and AA over three months fell within ±2 standard deviations of the expected mean difference, consistent with good reproducibility. Urinary levels of IL-6 during sleep predicted systolic but not diastolic BP between the AA and EA women. IL-6 was also associated with epinephrine, norepinephrine and cortisol excretion, and had a moderating effect on the ethnic differences in systolic and diastolic BP changes from work-sleep when norepinephrine was included as a covariate. These findings support previous studies that show that BP differences between AA and EA women may be mediated by differences in beta-adrenergic receptors. The results also support studies demonstrating that IL-6 potentiates stress hormone release and shows that IL-6 may influence the difference in BP variation between AA and EA women. This research was supported by NIH grant CA72457.