Angiotensin-converting enzyme (ACE) has two common genetic variants: the insertion (I) and deletion (D) forms. ACE levels are greater in subjects with the D allele, and several studies suggest superior endurance performance in subjects with the I allele. The authors recently reported the results of a 6-month exercise training protocol examining the effect of apolipoprotein E on the lipid response. The present report examines the relationship of ACE genotype and exercise adherence. DNA samples were available for 110 subjects: 14 I/I, 52 I/D, and 44 D/D. Baseline and change in maximal oxygen uptake, body mass index, skinfold thickness, and serum lipids did not differ by ACE genotype, but adherence to exercise training was higher in I carriers than in D homozygotes. These preliminary results suggest that ACE genotype affects exercise adherence and raises the possibility that superior endurance capacity in subjects with the I allele is related to a genetic propensity to adhere to an exercise regimen.