An experiment was conducted to measure the effects of exposure to heat or cold during incubation on the size of skeletal bilateral traits (face, wings, shank, tibia, and femur) and weights of heart and lungs of broiler embryos. Measurements were obtained at 10 and 18 d of incubation and at hatch on d 21. Treatments consisted of eggs incubated at 37.8degreesC throughout (control; C), cooled to 36.9degreesC for 6 h daily from d 0 to 8 (C0-8), heated to 39.6degreesC for 6 h daily from d 0 to 8 (H0-8), cooled to 21.0degreesC for 24 h on d 14 (C14), cooled to 36.9degreesC for 6 h daily from d 10 to 18 (C10-18), and heated to 39.6degreesC for 6 h daily from d 10 to 18 (H10-18). Although cooling and heating of eggs during incubation influenced growth of the skeletal traits on d 10 and 18, compensation generally occurred by the time of hatch. The developmental stability of bilateral traits varied with the specific trait, with those observed earlier in incubation tending to decrease by hatch.