OBJECTIVE To study the relationship between hypertension and the plasma levels of brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP), and to determine whether the plasma levels of BNP and CNP are correlated. METHODS A cross-sectional study of the plasma levels of BNP and CNP in hypertensive patients and normotensive controls matched for age and sex was performed. METHODS The hypertension research clinic in a teaching hospital and well-person risk factor screening clinics in general practice health centres. METHODS Fifty-four subjects (29 hypertensive, 25 normotensive controls) took part in the study after giving their informed consent. Hypertensive patients (n = 19) were paired with normotensive controls (n = 19) matched for age and sex to form a subgroup before analysis of the plasma. METHODS The plasma levels of BNP and CNP were determined by specific radioimmunoassays. RESULTS The mean plasma concentration of BNP was significantly higher in the hypertensive group than in the paired controls. In contrast, the mean plasma concentration of CNP was not significantly different in the hypertensive group than in the paired controls. Multiple regression analysis of all 54 subjects showed that the plasma level of BNP correlated significantly with age and systolic blood pressure, whereas the plasma level of CNP correlated significantly with sex, heart rate and alcohol intake. The CNP levels did not correlate significantly with either systolic or diastolic blood pressure, or with plasma brain natriuretic levels. CONCLUSIONS Hypertension is associated with raised BNP but not CNP plasma levels.