An inexpensive enzyme kinetics laboratory exercise for undergraduate biochemistry students is described utilizing tyrosinase from white button mushrooms. The exercise can be completed in one or two three-hour lab sessions. The optimal amounts of enzyme, substrate (catechol), and inhibitor (kojic acid) are first determined, and then kinetic data is collected in the absence and presence of the inhibitor. A Microsoft Excel template is used to plot the data and to fit the Michaelis-Menten equation to the data to determine the kinetic parameters V[subscript max] and K[subscript m]. The exercise is designed to clarify and reinforce concepts covered in an accompanying biochemistry lecture course. It has been used with positive results in an upper-level biochemistry laboratory course for junior/senior students majoring in chemistry or biology.