Nine patients with severe congestive heart failure were treated with a partial beta-1-agonist prenalterol for 9.6 months on average. Five of the nine patients improved with an increase in NYHA-functional capacity of one class. In four of these patients, the improvement was maintained for 12 months. Upon discontinuation, deterioration occurred only in one case; in the latter, improvement reoccurred on reinstitution of prenalterol treatment. Significant improvement on exercise testing, however, occurred only in two patients. Prediction as to which patients would benefit from oral prenalterol was not possible from the pretreatment haemodynamic variables; similarly, the effect of oral prenalterol treatment could not be predicted from the response to prenalterol given intravenously. A critical review of the methods for evaluation of therapeutic intervention in congestive heart failure concludes the article.