Population studies of Sceloporus jarrovi using mark—recapture procedures were conducted on two study plots near Portal, Chiricahua Mountains, Cochise Co., Arizona during the summer months of 1969 and 1970. Similar studies of Sceloporus poinsetti were conducted on a study plot near Mertzon, Irion Co., Texas during the summer months of 1968, 1969, and 1970. Series of these lizards were taken from areas near the study plots and autopsied to determine their reproductive condition. The reproductive cycle of both species involved mating in the fall, with parturition occurring the following June. A single litter was produced each year. S. poinsetti attained maturity during the second mating season after birth, at about 16—17 months, although approximately 60% of the S. jarrovi females matured in their first mating season at about 5 months. Female S. jarrovi which matured as yearlings produced an average of four young in their 1st year, whereas older females produced an average of 10.5 young (7—15). The increase in litter size with snout—vent length was one embryo per 3 mm of body length. S. poinsetti females produced an average of 10.4 young (6—23) with an increase of one embryo per 3 mm of body length. Body sizes of young at birth were 29—35 mm in S. poinsetti and 25—32 mm in S. jarrovi. Newborn of both species were larger than hatchlings of similar sized oviparous species of Sceloporus. Newborn of S. poinsetti from large litters were significantly smaller than newborn from small litters. Populations of both S. jarrovi and S. poinsetti had 50:50 sex ratios. In June, the ratio of yearlings to older animals was approximately 50:50 in S. poinsetti and 60:40 in S. jarrovi. Of the eggs ovulated, 4.5% died before parturition in both species. Percent annual mortalities of S. poinsetti and S. jarrovi were respectively 86% and 81% (newborn), 54% and 56% (yearlings), and 57% and 63% (adults). The life history strategy of S. poinsetti appears to be relatively K—selected. S. jarrovi is more r—selected than S. poinsetti but more K—selected than most oviparous species.