The effect of sodium dodecyl sulfate and sodium decylbenzene sulfonate on the chymotrypsin-catalyzed hydrolysis of N-acetyl-L-tyrosine ethyl ester was investigated. Pretreatment of the enzyme with sodium dodecyl sulfate produces inactivation which is dependent on the ratio of the surfactant to protein. Total loss of activity is achieved at a surfactant to protein (w/w) ratio of 15. Addition of chymotrypsin to a mixture of detergent and substrate does not affect the activity of the enzyme at low concentrations of sodium dodecyl sulfate. An enhancement in the activity is noted at higher surfactant concentrations, presumably due to the increase in the ionic strength of the reaction medium. The reaction of sodium decylbenzene sulfonate with chymotrypsin results in the formation of a series of complexes in an 'all or none' manner. Inactivation of the enzyme is noted initially at a surfactant to protein ratio of 1.0 and subsequently at ratios higher than 10. However, considerable activity is retained at surfactant to protein ratios of 3:5. The hydrolysis of N-acetyl-L-tyrosine ethyl ester is considerably influenced by the ionic strength of the medium. Increases in the ionic strength cause an enhancement in Vmax without affecting the affinity of the enzyme for the substrate.