Matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) may be involved in tissue remodelling in the primate corpus luteum (CL). MMP/TIMP mRNA and protein patterns were examined using real-time PCR and immunohistochemistry in the early, mid-, mid-late, late and very late CL of rhesus monkeys. MMP-1 (interstitial collagenase) mRNA expression peaked (by >7-fold) in the early CL. MMP-9 (gelatinase B) mRNA expression was low in the early CL, but increased 41-fold by the very late stage. MMP-2 (gelatinase A) mRNA expression tended to increase in late CL. TIMP-1 mRNA was highly expressed in the CL, until declining 21-fold by the very late stage. TIMP-2 mRNA expression was high through the mid-luteal phase. MMP-1 protein was detected by immunocytochemistry in early steroidogenic cells. MMP-2 protein was prominent in late, but not early CL microvasculature. MMP-9 protein was noted in early CL and labelling increased in later stage steroidogenic cells. TIMP-1 and -2 proteins were detected in steroidogenic cells at all stages. Thus, MMPs and TIMPs are dynamically expressed in a cell-specific manner in the primate CL. Early expression of MMP-1 is suggestive of a role in tissue remodelling associated with luteinization, whereas MMP-2 and -9 may contribute to later stage luteolysis. TIMP expression may control MMP activity, until declining at luteolysis.