Analysis of locomotor patterns of Amphibolurus cristatus, Crotaphytus c. collaris. Gambelia wizlizenii. Sceloporus u. undulatus and Cnemidophorus t. tesselatus shows that the basic speed gait is the trot. A complete locomotor cycle of Crotaphytus is described. Details of leg, tail and body action are given for the above species. Evidence is given to show that bipedal progression is best developed and more efficient in Amphibolurus than in iguanid lizards. Differences between quadrupedal and bipedal locomotion of lizards and mammals are discussed. A previous listing of 8 spp. of lizards habitually resorting to bipedal locomotion is augmented by 10 others. Bipedal lizards are subdivided into 2 groups based on habitat preferences.