Mouse collagenase cDNA was cloned and sequenced. The deduced amino acid sequence was compared to those of the other mammalian collagenases and related matrix metalloproteinases. These comparisons, as well as those of some enzymatic properties, show that the rodent (mouse and rat) interstitial collagenases are very similar but differ more from the other interstitial collagenases than does human neutrophil collagenase. This supports the hypothesis that the order Rodentia is an outgroup to the other eutherian (placental) mammalian orders.