In calculating pharmacokinetic parameters, Subjective bias may be induced by using the method of residuals. This paper reports a nonlinear least squares fitting program which may be adapted in APPLE II microcomputer. The program can not only increase the precision of estimated parameters, but also provide objective criteria e.g. Akaike's Information Criterion ( AIC ) for determining which kind of compartment model is most appropriate. Furthermore, the standard error of parameter is calculated which gives the variability of the estimation. The use of this program is guided on-screen prompts that display Some form of menu including the various types of compartmental models for intra and extravascular administration. The data can be stored or drawn out from the disk and the plot of curve fitting is readily feasible.