The average distance moved between captures (d) in a 10 x 10 live trap grid with 15.2-m spacing was determined for eight species of rodents in South Texas during January-July 1975 and 1976. Large samples yielded fairly precise estimates of d for cotton rats (Sigmodon hisPidus) (25.8 ± 0.58 m), deer mice (Peromyscus leucopus and P. maniculatus) (33.2 ± 2.50 m), fulvous harvest mice (Reithrodontomys tulvescens) (36.3 ± 1.92 m), and gray wood rats (Neotoma micropus) (20.7 ± 1.61 m). Generally, movements of adults were larger than those of juveniles and movements of males were larger than those of females. The data indicated a need to stratify the estimated area of trap grid influence by habitat for cotton rats and by yearly rainfall for gray wood rats for more accurate density estimates. The present data may be useful to other workers for determining the area of influence for lines or grids of traps.