We have developed a model for cloacal exstrophy in the chick embryo using the Cavitron AO 300 CO2 laser. Embryos between 68 and 76 hours of development have been injured caudal to the omphalomesenteric vessels in the region of the tail bud in ovo. This has resulted in the induction of cloacal exstrophy in 5 of 59 chicks that survived ten days after injury. Evidence from this model suggests that cloacal exstrophy is caused by early disruption of the cloacal membrane or that group of cells responsible for its subsequent development.