Using the indirect immunofluorescence method, autoantibodies (AB) of IgG and IgM classes were investigated in sera from 161 consecutive patients with essential hypertension and compared with those from 78 healthy normotensive subjects of the same composition by age and sex, and without any family history of hypertension. The frequency of one or more AB was as high in 78 untreated (15.3%) as in 83 treated patients (13.0%) and was in the controls 9.0% (n.s.). In the treated patients, the AB were associated with heart involvement (p less than 0.02). In the untreated patients, antinuclear antibodies of IgG class were associated with BP (p less than 0.01) and fundus grading (p less than 0.005). A family history of hypertension was found in 23.5% of the hypertensive males with AB and in 9.0% of the normotensive males (p less than 0.10). These results are discussed in relation to reports of an association of AB with cardiovascular diseases. It is concluded that the presence of AB in essential hypertension is not necessarily due to drug induction.