In order to check on the accuracy of the above calculations, an estimate of density was made for each species on the basis of trapping data. Trapping records kept for each animal were checked for the year 1963. More data on home ranges were obtained in that year due to higher population densities than in 1964. If an animal was caught four or more times in 1963, it was considered to be a resident; animals caught in both 1963 and 1964 were considered to be residents even if caught fewer than four times. Mice caught three times, with at least a month elapsing between the first and third captures, were considered to be probable residents. Other animals caught three or fewer times were considered to be migrants. In 1963, 15 individuals of _P. truei_ were caught four or more times, or in both years, and considered to be residents; six other mice were classed as probable residents. Of _P. maniculatus_, 18 individuals were classed as residents, and two as probable residents. Thus the trapping data for 1963 indicate that 21 individuals of _P. truei_ and 20 of _P. maniculatus_ were residents of the trapping grid. These estimates lie well within the estimated limits of density of each species, as calculated from data on home range while taking into account the relative proportions of available habitat for each species within the trapping grid. Analyses of trapping data indicate that the density of each species probably is overestimated by calculations of density based on home range data. Males and females of both species of _Peromyscus_ appeared to be highly individualistic in the amount of area they utilized. Some adult males of _P. truei_ covered large areas, whereas others were relatively sedentary. The same was true of young males of _P. truei_, although the younger males tended to have smaller ranges than adult males. Most pregnant or lactating females, of both species, tended to use smaller areas for their daily activities than did non-pregnant or non-lactating females. There were notable exceptions to this generality, for some lactating females had exceptionally large home ranges. Size of home range apparently was not influenced by the location of an animal's range within the grid. Far more data would be needed to correlate minor differences in vegetational associations with sizes of ranges in different parts of the grid. It is surprising that adults of _P. truei_ do not have larger home ranges than adults of _P. maniculatus_. _P. truei_ is the larger, more robust animal, capable of rapid running and occasional saltatorial bounding; individuals of this species can traverse large areas with ease. The semi-arboreal nature of _P. truei_ may explain why individuals of this species do not have larger ranges than individuals of _P. maniculatus_. _P. truei_ has a three-dimensional home range, whereas _P. maniculatus_ has a range that is two-dimensional only (excluding the relatively minor amount of burrowing done by each species).