Summary: Hypertension is a quantitative derangement of a physiological parameter rather than a disease and acceptance of this fact has greatly influenced the treatment of hypertension. Experience gathered over many years can be critically analysed to gain further information about the treatment of hypertension and the effect of different treatments on the complications of hypertension. The extent to which hypertension is a causative risk factor for coronary heart disease is still disputed, a lowering of blood pressure having not yet been conclusively shown to be invariably associated with a reduction in the incidence of coronary heart disease. On the other hand, a causative relationship with cerebro-vascular disease has been convincingly shown. This raises the possibility that, at least for coronary heart disease, the way in which blood pressure is lowered may be important. Many treatments for hypertension affect other parameters, e.g., electrolytes and plasma lipids, and it may be that a positive effect on blood pressure may be offset by a negative effect on another parameter. Evidence that this is indeed the case with diuretics has emerged from a number of large-scale trials. The cardio-protective effect of β blockers has also recently been extensively examined, although no clear conclusions have yet been reached. Primary prevention and secondary prevention are not the same, and positive results in one do not necessarily mean that the same drug will be effective in the other. A number of trials have been carried out to gain more information about the value of β blockers, but it is unlikely that conclusive evidence will emerge due to the small difference in the therapies compared and the relatively short duration of the trials.