Hematology is an important health indicator in birds, but the stress from capture or anesthesia can cause alterations in blood count. This study aimed to evaluate the differences found in blood counts among guans (Penelope obscura) under physical restraint and anesthetized with isoflurane. Thirty-two free-range guans from the Brazilian Institute of Environment and Renewable Natural Resources (IBAMA) Park were enrolled in the study. After physical restraint, blood samples were obtained from the ulnar vein and placed in heparinized tubes. The birds were anesthetized with isoflurane and after 45 min, when the animals were still anesthetized, a blood sample from the jugular vein was collected. Data were analyzed by paired t-test, and the differences were analyzed with Tukey's test. Decreases in red blood cell counts, hemoglobin concentrations, and packed cell volumes, and increased mean corpuscular hemoglobin concentrations were observed when animals were under general anesthesia. Decreases in total plasma protein, fibrinogen, and thrombocytes were detected after anesthesia. It was concluded that isoflurane influences the hematologic parameters, and those effects should be considered when interpreting hematologic values.