The purpose of this study was to investigate circadian changes in noradrenaline (norepinephrine) levels in patients presenting with congestive heart failure. Eighteen patients were investigated with a group mean age of 66 years, 12 in NYHA class III and 6 in class IV. The cause of the heart failure was ischemia in 7 cases, valvular in 1 case and idiopathic in the other 10 cases. The mean follow-up time of the disease was 3.9 years. Six healthy volunteers were investigated following the same protocol. Blood samples were taken while the patient was lying down over a period of 24 hours, after installing a peripheral venous catheter. The assay was carried out by means of high performance liquid chromatography with electrochemical detection. In the controls, the mean noradrenaline level (norepinephrine) was 220 +/- 62 pg/ml, with daytime peaks. The heart failure patients showed a high mean level (230 +/- 404 pg/ml), with less daytime variability than the controls (92% vs 127%; p < 0.05). The 8 a.m. value was reproducible, and there was close correlation between this value and the mean value for the 24 hours (p < 0.001). Thus, the morning sample provides a good estimation of the levels over the 24 hours.