Abbott Laboratories has developed a new software package (Abbottbase pharmacokinetic system or PKS package) that employs the principles of pharmacokinetics to assist clinical pharmacologists and clinicians in designing dosage regimens. This software, which runs on IBM PC compatibles, allows Bayesian estimation of individual pharmacokinetic parameters. The aim of the present study was to validate this new system in routine clinical practice for amikacin (40 intensive care unit patients) and theophylline (20 patients). By using the program one or more times during the treatment (50 cases for amikacin and 46 cases for theophylline), dosing recommendations were obtained in real time for all patients. The predictive performance (bias and precision) was assessed by comparing predicted drug concentrations with those measured 24-48 h after dosage recommendation. In the case of amikacin, precision and bias were computed separately for peak and trough levels. In all cases, no statistically significant bias was observed. Finally, our results demonstrate the accuracy of the program in predicting drug levels for amikacin and theophylline. Consequently, the PKS package is reliable for the choice of optimal dosage regimen for amikacin and theophylline.