The aim of this study was to evaluate retrospectively the outcome of 101 patients who were assigned to long-term therapy with propranolol (55 patients) or verapamil (46 patients) between 1980 and 1988. Baseline clinical, electrocardiographic, and echocardiographic data were similar in both groups. Exclusion criteria were the evidence of complex ventricular arrhythmias, a family history of the disease and/or sudden death, previous syncopal episodes, or left ventricular dysfunction. During a mean follow-up of 4 +/- 3 years (range: 1-9 years), side effects were more commonly recorded in patients who were treated with verapamil rather than in propranolol-treated patients (8 vs. 3, respectively), though the difference was not statistically significant. Sixteen patients (13 propranolol-treated patients and three verapamil-treated ones, p less than 0.05) died suddenly while on treatment. In addition, three patients who stopped verapamil because of adverse reactions died from heart failure after withdrawal, but before the end of the follow-up period. The assessment of total mortality on the intention-to-treat basis showed that death due to cardiac causes occurred in 13 propranolol-treated patients and in six verapamil-treated patients (ns). Thus, verapamil was more effective than propranolol in preventing sudden death during long-term therapy of "low-risk" patients with hypertrophic cardiomyopathy, though its administration was associated with the occurrence of non-sudden cardiac deaths and a high incidence of side effects.