This paper presents a computer program written in BASIC for fitting different enzyme inhibition kinetic models. The program, based on a nonlinear least-squares regression, can be run on any microcomputer with the CP/M operating system. Weighting of observed initial velocities is decided by the user by assessing constant variance, proportional variance or by incorporation of the variances calculated by a subroutine. The program also uses robust regression by bisquare weighting. All questions concerning data input, type of rate function, type of weight and the use of bisquare regression appear on the video display unit.