Long-term maintenance of captive populations and release of these animals into the wild is one approach to endangered species conservation. In this study, I used a traditional ethological technique, the open-field test, to assess captivity's effects on exploratory behavior, level of activity, and enclosure use in oldfield mice ( Peromyscus polionotus subgriseus ) upon introduction to a novel environment. The animals tested were from four populations collected from Ocala National Forest, Florida, and were held in captivity for varying numbers of generations: 35, 14, 2, and 0 (wild caught). The population 35 generations removed from the wild was behaviorally distinct from the other three populations. The mechanisms behind the differences are unclear. This study, however, is an example of how traditional behavioral methods can be applied to conservation problems. Whether captive populations are raised for lab studies or for captive breeding of endangered species, this study suggests that if they have been removed from the wild for more than 14 generations, they are likely to be significantly different from the wild counterparts of interest.