IN previous publications1,2, we reported that extracts of animal pancreas made with fluids of different pH exhibit varying elastolytic activity (e.u./gm.) on account of the presence of elastase inhibitor, which in the pancreas is bound to elastase3. In crude neutral solution, the activation of elastase may be carried out by acidification, dialysis or precipitation with ammonium sulphate1,2. In all these procedures the elastase is being liberated from elastase-inhibitor. It has been pointed out by us that two types of elastase-inhibitor exist, namely, one in the pancreas and another in the blood serum4. Whereas that from the pancreas dialyses in 24–32 hr. and can be demonstrated in the dialysate, that from the serum cannot be dialysed.