Specific and total activity of the digestive protease, chymotrypsin, was studied in cultured sharpsnout sea bream larvae (Diplodus puntazzo) for 35 days from hatching and in a variety of pH levels. Activity was detected upon hatching (2.8 +/- 0.34 mm total length), before the onset of exogenous feeding. Specific chymotrypsin activity exponentially increased from mouth opening on day 3 until day 25, then dropped until the end of the experiment. Total chymotrypsin activity sharply increased to day 10, then continued to increase, but slightly, until the end of the experiment. As expected, pH strongly affected both specific and total chymotryptic activity in the digestive tracts of larvae. Both were significantly lower when pH was acidic (1.5, 3.0, 4.0) than when it was alkaline (8.0, 9.0, 10.0) although there were no significant differences within either the acidic or the alkaline range. Our results indicate that chymotrypsin activity is capable of digesting protein before mouth opening and may be a valuable tool for better understanding the nutritional capabilities of young larvae.