A graphical method for determination of the type of enzyme inhibition and the dissociation constant (K_i) for an enzyme-inhibitor complex. The effect on the enzymic rate (v) is determined at two or more substrate concentrations, and over a range of inhibitor concentrations (I). In a plot of 1/v against I, data for each substrate concentration fall on straight lines that intersect at I=-K_i and 1/v=1/V_max (competitive inhibition), or that intersect on the abscissa (1/v=0) at I=-K_i (non-competitive inhibition). For uncompetitive inhibition, the lines are parallel.