A nesting box is provided for use with a metabolism cage. The nesting box comprises an enclosure for receiving a nesting dam. The enclosure has a top wall, a bottom wall and sidewalls. Either the top wall or one of the sidewalls includes an entrance/exit aperture. The entrance/exit aperture has a selected size that is selectively provided relative to a defined size of the nesting dam. The nesting box is formed of a substantially transparent material allowing observation of the nesting dam and pups without opening the box. The nesting box is adapted for use with different laboratory animals, such as mice, hamsters, gerbils, rats, guinea pigs, and rabbits.