Pancreata preserved in a solution containing ulinastatin may improve islet quality and quantity. This in vitro study was performed to investigate the efficacy of this agent to inhibit endogenous proteases (trypsin, chymotrypsin, and elastase) as well as its effects on thermolysin, liberase, neutral protease, and pancreas digestion switch samples. The EnzCheck Protease Assay Kit was used to measure the activities of these enzymes in the presence of drug at various concentrations (10, 25, 50, 100, and 200 U/mL) to determine the optimal conditions for inhibition/activation. The percentage of inhibition or activation was determined based on a comparison to controls using standard curves. At 100 U/mL the drug significantly inhibited trypsin (91%; P = .001), chymotrypsin (97%; P = .002), and elastase (43%; P = .01); however, inhibition of the switch samples was not significant (13%; P = .7). Serendipitously, ulinastatin at 10, 25, 50, 100, and 200 U/mL increased thermolysin activity by 9%, 123%, 149%, 172%, and 311%, respectively, and liberase activity by 35%, 27%, 44%, 51%, and 63%, respectively. In conclusion, ulinastatin displays dual functions to inhibit endogenous proteases and to increase neutral protease activity, possibly through allosteric effects. This activation of neutral proteases may significantly enhance collagenase activity, thereby resulting in higher islet yields.