This is a metaanalysis of all available studies as of December 1990 that have evaluated the effect of antihypertensive pharmacologic therapy on left ventricular structure examined by echocardiography. We applied preset inclusion criteria to the analysis. A total of 109 studies comprising 2357 patients (28% previously untreated) with an average age of 49 years (range 30 to 71) were included. Overall left ventricular mass (LVM) was reduced by 11.9% [95% confidence interval (CI) 10.1 to 13.7] in parallel with a reduction of mean arterial pressure of 14.9% (CI 14 to 15.8). To differentiate between first-line therapies and to adjust for differences between studies, we performed ANCOVA. Angiotensin converting enzyme (ACE) inhibitors reduced LVM by 15% (CI 9.9 to 20.1), β-blockers by 8% (CI 4.8 to 11.2), calcium antagonists by 8.5% (CI 5.1 to 11.8), and diuretics by 11.3% (CI 5.6 to 17). When we calculated LVM using the same formula for all studies the absolute reductions in grams were 44.7 g with ACE inhibitors, 22.8 g with β-blockers, 26.9 g with calcium antagonists, and 21.4 g with diuretics. Except for diuretics, all therapies mainly affected wall thickness, while diuretics predominately reduced ventricular diameter. In conclusion, this metaanalysis shows that ACE inhibitors, β-blockers, and calcium antagonists all reduce LVM by reversing wall hypertrophy, and that the effect is most pronounced with ACE inhibitors. Conversely, diuretics reduce LVM mainly through a reduction of left ventricular volume. Based on these data, we hypothesize that ACE inhibitors are more effective than other first-line therapies in reducing LVM. However, this theory and its possible prognostic implications need to be evaluated in controlled prospective trials. Am J Hy-pertens 1992;5:95-110