The leukocyte count: a predictor of hypertension. In an exploratory study of 1031 persons observed to progress from normotension to essential hypertension and 1031 matched subjects who remained normotensive, the initial leukocyte count (WBC) was found to be related to the development of hypertension, with risk increased 40% (95% confidence interval 12-82%) in persons in the highest as compared to the lowest quartile of WBC. This relationship proved to be largely independent of body mass index, body fat distribution, alcohol and tobacco consumption, and parental history of hypertension. An increased WBC may reflect greater sympathetic tone or may directly increase peripheral vascular resistance by impeding circulation through small blood vessels. If confirmed, this study adds another condition to the growing list for which the WBC is predictive. This simple, cheap test should be considered for inclusion in prospective epidemiological studies of many different diseases. 