A procedure, based on the Gauss-Newton method for non-linear regression, has been developed to obtain enzyme kinetic constants from the analysis of progress curve data. Rules are presented which greatly simplify the derivation of the necessary equations. The method has been applied to the reactions catalysed by prephenate dehydratase, acid phosphatase and lactate dehydrogenase and has yielded values for kinetic parameters which agree well with those obtained from steady-state rate measurements.