Screening methods for the rapid determination of Y chromosomal ploidy (peripheral blood leukocyte fluorescence analysis) will be applied to two populations of adult males: (1) Those under treatment for hypertension in one of the participating centers in the national Hypertension Detection and Follow-up Program; and (2) those in the national Health and Nutrition Examination Survey. Data so derived will shed light on the association of Y aneuploidy with a chronic disease of great economic importance (hypertension), and will also establish the prevalence of Y aneuploidy in heterogeneous, ambulatory population not afflicted with any specific illness.