The expression and regulation of metalloproteinases-2,-9(MMP-2,-9) and their tissue inhibitors TIMP-1,-2,-3mRNA were studied in this experiment. In the PMSGhCG primed pseudopregnant rat, MMP-2,-9mRNA levels were the highest at Day 1, decreased from Day 4, and reached the minimal level at Day 8, then increased at Day 14; no significant changes were observed in TIMP-2 mRNA expression from Day 1 to Day 14; TIMP-3 mRNA expression was the lowest at Day 1, increased from Day 4, reached the maximal level at Day 8, and persisted to Day 14. TNF-a could significantly increase the expression of MMP-2,-9 and TIMP-1 mRNA in the in vitro perfused pseudopregnant CL, and decrease the expression of TIMP-3 mRNA, but had no effect on TIMP-2 mRNA expression. The results indicate that MMP-2,-9and TIMP-1,-2,-3 might be involved in the regulation of CL function and maintenance of CL structure via their coordinated gene expression. TNF-a could inhibit luteal regression via increasing MMP-2,-9andTIMP-1 mRNA in the in vitro perfused pseudopregnant ovary.