This study serves to further define the capabilities of the whole embryo culture system using the known teratogen, Hydroxyurea (HU). An initial in vivo study was performed where by day 9 pregnant mothers were injected IP with 300 mg/kg HU. Dams were sacrificed two days later and embryos were analyzed for malformations and total embryonic protein. In addition, the peak plasma value from injected dams was found to be approximately 300 micrograms/ml with a plasma half-life of 30 minutes. These values were then reproduced in the culture system with similar results noted in cultured embryos with respect to the type of malformations found. Additional in vitro experiments were performed varying both exposure time and drug level concentrations. Results indicate that both of these parameters are important considerations when designing in vitro experiments.