Hematological and blood chemical values were determined for wild and captive mallards, Anas p. platyrhynchos, for the late spring period prior to remige moult through early fall migration. Hemoglobin, packed cell volume, erythrocyte and total leukocyte counts, as well as the number of heterophils and lymphocytes, declined significantly during and after remige moult compared to values recorded prior to remige moult. During fall migration mallard drakes had elevated levels of glucose and uric acid. No significant changes were observed in total protein, alkaline phosphatase, glutamic oxaloacetic transaminase or creatine phosphokinase in pre- or post-moult periods. The hematological and biochemical values should prove useful in providing background information on mallard drakes, and documenting baseline data for intra and interspecies comparisons with diseased birds.