During surimi processing, cathepsins B and L activities in minced, leached and NaCl-ground meats were 6.02, 5.23, and 4.07 units/g, respectively. About 80% activity remained in surimi after 8 wk storage at Ϫ40ЊC suggesting that these proteinases were stable and difficult to remove. At 40Њϳ55ЊC, pH 6.5ϳ7.5, cathepsins B and L and purified cathepsin B had high hydrolytic activity on myosin heavy chain (MHC). The strength of surimi gel with cathepsins B and L or with purified B decreased (pϽ0.05) after 2 hr incubation at 55ЊC. This suggested that the residual cathepsins B and L had MHC-degrading activity and consequently caused gel softening.