Cross-matching of the giant tortoise of San Cristóbal (Chelonoidis chathamensis) was employed to determine if erythrocyte agglutination occurs in individuals with no transfusion history after exposure to plasma from a conspecific individual. The main islands in the Galápagos archipelago are inhabited by unique species of tortoises. On the largest island, Isabela, there are multiple species isolated by volcanic formations creating unique separate ecosystems. With plans to begin the reintroduction of C. chathamensis into the wild, as well as the recent rediscovery of the Fernandina giant tortoise (Chelonoidis phantasticus), appropriate veterinary care is paramount, and having every medical contingency, especially vehicular/tortoise interaction, under consideration is important. Cross-matching the San Cristóbal giant tortoise was a first step in exploring the compatibility of blood transfusions between conspecifics. Blood was drawn from the jugular vein of 20 juvenile tortoises with the use of a heparinized syringe and each sample was coded. The blood was centrifuged, the erythrocytes washed (five times), and then the erythrocyte pellet and plasma were used for the major cross-match procedure. The erythrocytes represented the “donor” tortoise and the plasma represented the “recipient” tortoise. Each tortoise was cross-matched against itself as an auto control and then 1–5 times against another randomly assigned individual at two incubation temperatures, 23°C (73.4°F) and 34°C (93.2°F). No agglutination was found in any of the trials. As predicted, fibrin and thrombocyte clumps occurred in all trials. Additional research that includes different species of tortoises is the next important step to enhance our knowledge of antigen compatibilities.