The kinetic constants for irreversible enzyme inhibition are determined by non-linear least-square regression using a new optimisation technique. An analysis is given of how calculation of the dissociation constant and the unimolecular rate constant is affected both by the inherent error involved in fitting an exponential curve to the plot of product concentration against time, and by the ill-conditioned nature of the equations relating these constants to the parameters of the exponential. The analysis is applied to simulated sets of product concentration curves.