Evidence indicates that matrix metalloproteinases (MMPs) are essentially involved in the postpartum involution of the uterus. As little information exists about the gene regulation of those MMPs in the uterus, this study aimed to characterize the time course of messenger RNA (mRNA) levels of rat collagenase (MMP-13) and matrilysin (MMP-7) in virgin, late pregnant (18th and 21st day), and postpartum rats (1, 2, 3, and 4 days postpartum). Rat collagenase (MMP-13) mRNA levels were very low in virgin and pregnant animals, but increased transiently 30-fold postpartum, reaching a maximum on the second day postpartum. The temporal course of mRNA levels of matrilysin (MMP-7) shows similarity with that of collagenase mRNA levels, but at any stage the abundance of matrilysin mRNA was at least 100-fold higher than that of collagenase. In virgin animals, matrilysin mRNA levels were dependent on the estrous cycle, being 3- to 4-fold higher in the estrous and diestrous stages than during metestrus. MMP-7 shows an approximately 25-fold induction when comparing the mRNA levels in late pregnancy and 2 days postpartum. In cervexes of virgin, pregnant, and postpartum groups, collagenase mRNA was not detectable. Matrilysin in cervix shows temporal mRNA expression similar to that in uterus, with a maximum on day 1 postpartum. In cervix, we found a 14-fold induction when comparing levels in late pregnancy and those 1 day postpartum. Taken together, our findings suggest that the increased activity of MMPs in the postpartum uterus is due to a strong increase in the mRNA levels of MMP-13 and MMP-7.