The effect on the heart of a combination of high blood pressure and chronic alcohol ingestion was studied in spontaneously hypertensive rats (SHR) fed ethanol in their drinking water in concentrations of 0%, 5% and 20% for sixteen weeks. Normotensive Wistar rats were used as controls (NCR). In addition some SHR were given alcohol for a shorter period of eight weeks at the end of which time there were no significant differences in mean arterial blood pressure between the groups. After sixteen weeks of ethanol the mean arterial pressure had fallen in those SHR receiving 20% ethanol to 136 +/- 24 mmHg compared to control (180 +/- 27 mmHg; P less than 0.001). This was associated with a lower left ventricular (LV)dp/dt (control 4800 +/- 872 mmHg sec-1; 20% ethanol group = 3450 +/- 1588 mmHg sec-1; P less than 0.025) and a reduced LV weight (corrected for body weight) due to an apparent lack of development of LV hypertrophy between eight and sixteen weeks. Similarly LV volume (corrected for LV weight), did not change from eight weeks to sixteen weeks in those SHR receiving 20% ethanol in contrast to the 0% ethanol SHR group in whom LV volume fell as LV hypertrophy developed. 5% Ethanol had no significant effect on mean arterial pressure, LV peak dp/dt, LV weight or LV volume. In the NCR ethanol had little effect on mean arterial pressure but those receiving 20% ethanol had significantly smaller LV volumes without any increase in LV weight probably reflecting blood volume depletion. Ethanol did not produce any blood pressure elevation in the NCR. No rats (SHR or NCR) developed overt heart failure or a typical cardiomyopathy. However, this study has shown that a high intake of ethanol reduces the blood pressure of a hypertensive rat most likely by its direct toxic action on the myocardium. Thus with chronic alcohol ingestion hypertension can be masked but may still contribute significantly to the development of myocardial disease.