Perturbation of neural crest cell migration has been implicated in the pathogenesis of conotruncal malformations (CTMs). Bis-Diamine (BD) chelates Zinc (Zn), which is a physiologic inhibitor of apoptosis. When BD is administered to gravid dams on days E10 and E11, CTMs are produced in the pups. Objective: We tested the hypothesis that BD interferes with neural crest cell migration by causing these cells to undergo apoptosis by inducing transient Zn deficiency. Methods: Bis-Diamine (200 mg) was administered to timed-gestation dams by gavage on days E10 and E11. Control dams received the carrier. Embryos were harvested on day E12. Regions of embryonic cell death were determined by Nile blue sulfate (NBS) vital staining. Serum Zn concentrations were determined by atomic absorption. Alkaline phosphatase (AP) activity was used as a sensitive marker of Zn nutriture. Activity of AP was measured in maternal serum using a standard clinical assay and in embryo homogenates by absorption spectrophotometry. Results: Vital staining of BD-exposed embryos revealed increased uptake of NBS relative to controls in the region of the branchial arches and developing outflow tract. Exposed and control dams had similar serum Zn concentrations before and after treatment. Serum AP activity in control dams demonstrated a normal pregnancy-associated rise of approximately 25% from day E10 to E12. In contrast, AP activity in BD-treated dams decreased 25%(P<0.01). Activity of AP in homogenates of BD-exposed embryos was reduced by 35% relative to controls (P<0.001). Conclusions: Chelation of Zn by BD during a critical window of time may induce CTMs by prematurely halting migration of cardiac neural crest cells into the developing outflow tract. Bis-Diamine appears to exert its effect by removing Zn, which is an apoptosis inhibitor.