Presence or absence of nesting behavior during spontaneous or hormone-induced oviposition was determined in captive, oviparous lizards (Anolis carolinensis and Sceloporus undulatus). The occurrence of nesting behavior [digging of a nest cavity, covering the egg(s) with substrate] was determined directly by observation of ovipositing females as well as indirectly by whether eggs were covered (buried). Under uncrowded conditions in large terraria, most females of both species nested. However, under crowded conditions (S. undulatus), or in small cages (A. carolinensis), females oviposited without displaying species-typical nesting behavior. Facultative suppression of nesting behavior during oviposition can occur in nature as well, and this inhibition of behavior may be adaptive. We hypothesize that the absence of nesting behavior in viviparous lizards may be controlled by physiological mechanisms similar to those that control facultative suppression in closely related oviparous species.