This is the most common species of the genus _Peromyscus_ in Tamaulipas. It and _Liomys irroratus_ are the two rodents most easily trapped throughout the state. In general _P. l. texanus_ occurs in forested and brushy areas especially under 1200 feet in elevation, as was noted in the Sierra de Tamaulipas, where _P. l. texanus_ was taken commonly at elevations of up to 1200 feet. Above this elevation the species was rare and _P. pectoralis_ and _P. boylii_ were more abundant than at lower elevations. The three specimens of _P. l. texanus_ from 12 kilometers north and four kilometers west of Ciudad Victoria were trapped in a line of 110 traps set near tree stumps. Small burrows in the ground were noted here. The forest at this locality was composed of mesquite, ebony, acacias, a few yuccas and "nopales" (= cactuses); the ground was covered by cat claw. Of the many young taken, 15 specimens were saved from Ejido Santa Isabel where _P. leucopus_ was abundant in an area of chaparral consisting of wild "tomate," "zapote," "huizache" and "salvadora." Most of the specimens caught at this locality were taken between 7:30 and 9:30 p. m. in traps baited with a mixture of rolled oats, peanut butter and banana. Specimens from 53 kilometers north of El Limón were taken along with _Liomys irroratus_; the specimen from two kilometers west of El Carrizo was trapped near a dead mesquite log. _Reitrodontomys fulvescens_ was taken in the same area. Four specimens of _P. leucopus_ were taken at Rancho Pano Ayuctle, around a big pile of old firewood in an abandoned sugar mill. At the locality six miles north and six miles west of Altamira, _P. leucopus_ was found in cultivated fields and along the grassy roadsides; in the vicinity of Tampico specimens were taken in an area of forested cactus-thorn. The specimen from seven kilometers south and two kilometers west of San Fernando was found in a trap set at the base of "nopal" cactus, which was surrounded by bushes and small trees (10-12 feet high). Breeding records are as follows: Rancho Pano Ayuctle, on February 15, one female carried 2 embryos of 23 mm. in crown-rump length; Jaumave, July 26 to 29, five females, averaging 4.6 (3-6) embryos of 7 (3-15) mm., two females lactating, one on May 25 and the other on July 26; Ejido Santa Isabel, on January 20 to 25, three females lactating; Soto la Marina, on May 16, one female lactating. Average weights were as follows: from Jaumave four pregnant females, 28.0 (25-33), eight males, 23.4 (21-27); from the Sierra de Tamaulipas, eight females non-pregnant, 21.2 (18-26), 14 males, 22.0 (19-27); from 6 mi. N, 6 mi. W Altamira, six males, 23.5 (21-27).