Abstract The duck eggshell has the reputation of being more permeable than that of the domestic hen. If this is true, the developing embryo could be at greater risk from xenobiotic agents, since toxicants picked up on the feathers could be transferred to the embryo during incubation. This study looked for such an effect on the developing embryo after the application of aldicarb to the eggshell. At 72 hr, the eggs were painted with 3, 7, 11, or 15 μ M aldicarb in 500 μl water. The eggs were then incubated to Day 24. The gross morphological measurements were then recorded. A similar study was made using domestic hen eggs; these were treated after 36 hr incubation and incubated to Day 17. Direct injection into the yolk sac of both species was used for further comparison. There was a statistically significant reduction ( P < 0.01) in the middle web toe length with 11 and 15 μ M aldicarb and the tarsometatarsus length with 7, 11, and 15 μ M. Compared with the duck control group, the group given 15 μ M aldicarb had reductions of approximately 8% in the tarsometatarsus and approximately 9% in the middle web toe. No statistically significant changes were produced in the chick embryos.