Reproduction, mortality rates, dispersal, and survival of young lions are among the most basic factors affecting lion populations. The Texas Parks and Wildlife Department (TPWD) initiated a research study to investigate home ranges, population dynamics, genetic variability, and diets. We captured 19 mountain lions (Felis concolor) on Big Bend Ranch State Park (BBRSP) 22 January 1993 through 9 March 1995, using trained hounds or leg-hold snares. All captured lions were examined, aged and sexed, and a series of body measurements were recorded. Two lions— 1 adult female and 1 subadult male—died during capture. A subadult male orphaned as a kitten and sent to a wildlife rehabilitor was returned to the study area, but was later killed off the study area. Fifteen lions—5 adult females, 1 subadult female, 7 adult males and 2 subadult males—were fitted with radio transmitters. Three of the collared lions—1 adult female and 2 adult males—were killed north of the study area. Collared lions were monitored from the ground and fixed-wing aircraft. We recorded 506 locations and delineated home ranges for 10 collared lions. Home ranges of males varied from 316-597 km2, while those for females ranged from 167 to 505 km2. Fecal analysis indicated collared peccary (Tayassu tajacu), mule deer (Odocoileus hemionus), and lagomorphs (Lepus spp.) were the most important prey species in descending order of frequency of occurrence. Data will continue to be collected for another 2 years.