The effects of exogenous transforming growth factor beta (TGF-beta) on chick limb development in vivo were studied by implanting carriers of TGF-beta 1 into developing wing buds. Agarose beads were soaked in solutions containing TGF-beta 1 and implanted into wing buds at stages 18 to 27. Localized application of TGF-beta 1 to distal regions of the wing bud caused specific skeletal elements in the limb to be reduced or absent. The particular proximal-distal limb element affected depended on the stage at which the bead was implanted. Position of the bead in the anterior-posterior axis also influenced the pattern of affected structures. Experiments in which TGF-beta 1 beads were implanted and then removed at 24- and 48-hr intervals indicate that there are specific periods during which a skeletal element appears to be sensitive to the effects of exogenous TGF-beta 1. In a few cases, beads placed in proximal positions in later staged limbs resulted in formation of ectopic cartilage near the bead. These results suggest that exposure to exogenous TGF-beta 1 in vivo influences the development of skeletal elements in the chick limb in a stage- and position-dependent manner.