Hypoxic effects on embryonic metabolism and growth of Florida red-bellied turtle (Pseudemys nelsoni) embryos were studied. Eggs were assigned to either normoxic (21% O2) or hypoxic (10% O2) treatment on day 21. Oxygen consumption (VO2) and embryonic mass were measured periodically. On day 21 and 33, critical oxygen tension (Pc) of embryos and morphometry of blood vessels in chorioallantoic membranes were measured. Although embryos exposed to normoxia increased VO2 and mass at a rate greater than those in the hypoxic condition during incubation, both groups hatched at the same time. Hatchlings from the hypoxic treatment had elevated hematocrit and greater relative dry ventricular mass compared to hatchlings from the normoxic treatment. The Pc of hypoxic embryos was significantly lower than normoxic embryos on day 33 (P < 0.001). Morphometric comparison of blood vessels in chorioallantoic membranes revealed no significant differences except in length density on day 33 (P < 0.05). It is concluded that exposure to chronic hypoxia resulted in retarded growth, depressed metabolism, comparable incubation period, and reduced hatchling mass. In addition, embryos exhibited some physiological plasticity which allowed increased oxygen transport in response to hypoxia.