Hematologic and biochemical reference ranges for two captive populations of northern bald ibises (Geronticus eremita) were compared. The first consisted of 11 birds at an in-situ breeding colony in Bireçik, southern Turkey. The second consisted of 27 birds housed at the Durrell Wildlife Conservation Trust in Jersey, British Channel Isles (UK). Blood samples were collected in February 1992 by basilic venipuncture under manual restraint. Bireçik birds had higher packed cell volumes and red blood counts but lower white blood cell and lymphocyte counts than Jersey birds. Bireçik birds also had higher total protein, albumin, total globulin, calcium, phosphorus, blood urea nitrogen, and total bilirubin values; higher albumin to globulin ratios; but lower uric acid values and calcium to phosphorus ratios than Jersey birds. Finally, Bireçik birds had higher lactate dehydrogenase but lower gamma glutamyl transferase values than Jersey birds. Male Jersey birds had higher calcium and alkaline phosphatase values, but lower white blood cell and heterophil counts than female Jersey birds. The apparent differences between the two populations are not thought to be biologically significant and may be related to diet and state of hydration.