Data were collected on 433 black medical students at Meharry Medical College (MMC) and 573 white medical students at The Johns Hopkins University School of Medicine (JHMS) during the period of 1958 through 1965 consisting of baseline measurement of some possible precursors of hypertension. Similar methods were employed in both cohorts. Comparison as to prevalence and significance of hypertension precursors revealed the following: Black males had significantly higher casual and resting blood pressures than whites (p less than 0.01); and higher mean changes in blood pressure following the cold pressor test. White males had a significantly higher mean change in heart rate following cold pressor test (p less than 0.01). Upon exercise black males had significantly higher mean change in blood pressure and heart rate (p less than 0.01). There appears to be more blood pressure lability in blacks as indicated by higher mean SBP + DBP changes following the cold pressor test, and by mean pulse pressure level at peak exercise. The difference in blood pressure lability observed between blacks and whites in young adulthood may be one of the earliest identifiers of later differences in the incidence of hypertension. However, of even more importance is the difference in blood pressure levels between the two groups, though both are normotensive.