Abstract
Summary 1. Plague which was first demonstrated in New Mexico in 1938 has apparently been present in Rio Arriba County for 6 years. 2. During a 14-week study in 1948, 3,298 animals were collected from which 4,650 fleas, 337 ticks and 38 lice as well as 3 tissue samples were obtained. 3. Plague was isolated 18 times from tissue and ectoparasites of prairie dogs and twice from ectoparasites from marmots. Indirect evidence of plague in smaller rodents was obtained from a study of population numbers.