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