Our results reveal the difference in the expression patterns of MMPs and TIMPs during follicle development between normal and miniature pigs. MMP-9 was highly expressed in In both normal and miniature pigs, the activity of gelatinases tended to be low in developing follicles; however, it was strongly expressed in the Graafian follicles of normal pigs. These results are consistent with the findings of Curry and Osteen (2001). Gelatinase activity was also detectable in the Graafian follicles of miniature pigs; however, it was lower than that in normal pigs. After ovulation, gelatinase activity was higher in the ovulated follicles of normal pigs than in those of miniature pigs. Gelatinase activity was higher in ovulated follicles than in developing and Graafian follicles. Since gelatinase activity remained high during ovulation, it can be speculated that the surge in luteinising hormone (LH) levels triggers rapid ECM restructuring and apoptosis in follicular cells. During this process, ruptured follicles are effectively reorganised into the corpus luteum (Hagglund et al. 2001). It is likely that both relative paucity of follicular maturation-promoting MMP-9 and elevated expression of apoptosis-inducing MMP-2 may contribute to the compromised fertility of miniature pigs.