Cardiac output was determined in 42 young essential hypertensives (15 to 25 yrs); values ranged from 3.86 to 10.30 L./minute. These differences were not related to magnitude of volemia. Correlation of output to weekly blood pressure average (BPav) was not significant; its relationship to intraarterial pressure (BPia) was not significant in 21 patients aged 20 to 25 and of borderline significance in 13 aged 15 to 19. Blood pressure changes associated with the study (BPia--BPav) were also not consistently related to cardiac output. Six patients had systolic hypertension; only one had elevated stroke volume. These results outline as complex a picture in young essential hypertensives as in older subjects.