Background. Homozygous carriers of the D allele of the angiotensin-converting-enzyme (ACE) gene have been reported to be at increased risk for various cardiovascular disorders, including left ventricular hypertrophy. We investigated the potential role of the ACE gene in influencing left ventricular mass. Methods. Quantitative echocardiographic data and DNA samples were available for 2439 subjects from the Framingham Heart Study. ACE genotypes were determined by an assay based on the polymerase chain reaction. (The D allele of the ACE gene contains a deletion, whereas the / [insertion] allele does not.) Left ventricular mass and the prevalence of left ventricular hypertrophy, adjusted for clinical covariates, were analyzed according to genotype. Genetic linkage between the ACE locus and left ventricular mass was evaluated by quantitative analysis of pairs of siblings. Results. The ACE genotype was associated neither with left ventricular mass nor with the prevalence of left ventricular hypertrophy. Mean (±SE) left ventricular mass (adjusted for sex) among subjects carrying the DD, DI, and II genotypes was 165±1.6, 165±1.3, and 166±2.0 g, respectively (P = 0.90). The prevalence of left ventricular hypertrophy among the three genotype groups was 15.6 percent, and 15.6 percent, respectively (P=0.36), and the adjusted relative risk of left ventricular hypertrophy associated with the DD genotype was 1.10 (95 percent confidence interval, 0.86 to 1.19). Linkage analysis in 759 pairs of siblings using both the ACE D/I marker and a microsatellite polymorphism at the neighboring locus for the human growth hormone gene failed to support any role of ACE in influencing left ventricular mass. Conclusions. The ACE genotype showed no association with echocardiography determined left ventricular mass, nor did it confer an increased risk of left ventricular hypertrophy. We found no appreciable role of the ACE gene influencing left ventricular mass.