A new chamber designed to evaluate the sexual behavior of rats was found to have distinct advantages over chambers typically described in the literature. The new testing chamber is narrow, which maintains a male and female rat in the optimal orientation for the observer to view sexual behavior, i.e., in the side view. Moreover, the chamber consists of an upper and lower level, which allows the females an avenue of escape from the male. In Experiment 1 it was shown that use of the chamber increased the reliability of data gathered in evaluating the lordosis behavior of female rats. In Experiment 2 it was shown that the new chamber could be used to evaluate the pacing of copulation by female rats.