In this paper, we examine the association between polymorphisms of the angiotensin-converting enzyme (ACE) and muscle-specific creatine kinase (CKMM) genes, and the actual performance status observed in professional cyclists capable of completing a classic tour stage race such as the Giro d'Italia, Tour de France, or Vuelta a Espana. To accomplish this, we compared the frequencies of the ACE and CKMM genotypes/alleles in 50 top-level Spanish professional cyclists that have completed at least one of these events to 119 sedentary controls, and 27 elite (Olympic-class) Spanish runners. The genetic polymorphism at the CK-MM locus was detected with the NcoI restriction endonuclease. The results of our study showed that the proportion of the DD genotype was higher in cyclists (50.0 %) than in the other two groups (p < 0.05), the proportion of the ID genotype was higher in controls (46.2 %) than in the other two groups (p < 0.05), and the proportion of the II genotype was higher in runners (40.7 %) than in the other two groups (p < 0.05). The proportion of the D allele was higher in both cyclists (65.0 %) and controls (57.6 %) than in runners (46.3 %) (p < 0.001), whereas the proportion of the I allele was higher in runners than in the other two groups (p < 0.001). No statistical differences were found for CKK-MM- NcoI. We conclude that in top-level professional cyclists capable of completing a classic 3-wk tour race, the frequency distribution of the D allele and the DD genotype seems to be higher than in other endurance athletes such as elite runners (in whom the I allele is especially frequent).