Recording the times of dosage administration and serum sampling by trained personnel resulted in significantly greater adherence to the protocol of therapeutic drug monitoring and in significantly greater precision in the achievement of desired serum concentration goals of aminoglycoside therapy than when relatively untrained personnel recorded it as a comparatively unemphasized part of their job. This was true even when only data of peak and trough serum concentrations were used. This study demonstrates that thoughtful data collection by appropriately trained nursing, pharmacy, or other clinical personnel is an essential part of therapeutic drug monitoring and plays a significant role in the optimal individualization of drug dosage regimens for patient care.