Lesser prairie chickens (Tympanuchus pallidicinctus), now rare though increasing in numbers in Colorado, were once fairly common in the southeastern part of the state, particularly in the area south of the Arkansas River. Information indicates that this species was probably once found in at least six counties: Baca, Prowers, Bent, Kiowa, Lincoln, and Cheyenne. Populations are thought to have occurred in earlier days in both the mixed prairie plant communities and the sand sagebrushgrassland plant communities. The species has been observed in Colorado during the period 1959 through 1962 only within the sand sagebrush-grassland plant communities and bordering cultivated fields. A major reduction in lesser prairie chicken range and numbers in Colorado apparently coincided with the general pasture depletion during the dust-bowl conditions of the 1930's. Populations have been censused through spring counts of cocks on booming grounds from 1959 through 1962. The numbers of cocks counted on the grounds have steadily increased over the 4-year period from 6 on three grounds in the spring of 1959 to 104 on thirteen grounds in the spring of 1962. Practices which have benefited the species in recent years include improved grassland management through rotation of pastures, moderate livestock use, and grass reseeding programs. Improved moisture conditions have also benefited the species. This paper presents the results of a basic inventory study on the lesser prairie chicken in Colorado. The investigations resulted from a lack of knowledge of the species by the Colorado Department of Game, Fish and Parks and from interest in the species by U. S. Forest Service personnel of the Comanche National Grasslands, with headquarters in Springfield, Colorado. The U. S. Forest Service controls approximately 260,000 acres of grazing lands in southern Baca and southeastern Las Animas counties. These lands were purchased from private landowners during the dust-bowl days of the 1930's. Many of these tracts are located within historical lesser prairie chicken range. Scattered sightings of prairie chickens by landowners and others during recent years indicated the species was still found in some areas in southeastern Colorado prior to the initiation of the study. I wish to thank E. E. Miller, U. S. Forest Service, Springfield, Colorado, and J. H. De Vore, U. S. Forest Service, Elkhart, Kansas, for their interest and assistance during the study; W. D. Snyder, Colorado Department of Game, Fish and Parks, Springfield, Colorado, for assistance in the field work of locating and counting populations; F. F. Copelin, Oklahoma Department of Wildlife Conservation, for va uable advice on census techniques and habits of the species; and Dr. A. M. Bailey, Denver Museum of Natural History, for historical information.