The present study was a retrospective, case-control design aimed at evaluating whether the clinical pharmacokinetic service (CPS) is cost-effective, as assessed by lengths of hospital stay and aminoglycoside therapy, incidence of a decrease in renal function, and time for resolution of infection as determined by vital signs. Forty-six patients were entered into this study, and were matched by defined criteria. The results of the study demonstrated a six-day difference in hospital stay for the CPS group (p less than 0.05). Length of aminoglycoside therapy was 33 hours shorter for the CPS group. Additionally, the time necessary for resolution of the infection was significantly shorter for this group, as assessed by vital signs returning to normal or baseline. Three patients in each group expired. Two patients in the CPS group and five in the control group developed aminoglycoside-associated increases in serum creatinine. No significant difference was found between the two groups in age, weight, or APACHE II score. Additionally, the two groups were similar with respect to concomitant diseases and concomitant antibiotics used. The approximate cost of the CPS was calculated as $56 per patient. Use of the CPS decreasing hospital stay by six days (mean $1875/patient) would translate to an annual savings of $654,375 in hospital charges, assuming 365 patients received aminoglycoside therapy per year.