Antibodies against herpes simplex virus (HSV) and cytomegalovirus (CMV) were examined in sera from 132 patients with essential hypertension and 54 normotensive healthy subjects of the same age and sex. Prevalences of HSV and CMV antibodies (titre greater than or equal to 4) were equal in patients and controls. A HSV antibody tire greater than or equal to 64 was found in 39.5% (17/53) of patients with WHO stage III hypertension, in 26.2% (22/85) of patients with stage I-II hypertension, and in only 9.4% (5/54) of normotensive subjects (p less than 0.0005). The HSV antibodies were mainly of type 1. No association between CMV antibodies and vascular complications could be demonstrated.