The therapeutic drug monitoring begins to extend from specialized laboratories into the practitioners office. A systematic approach to these new problems is, therefore, recommended, following these guidelines: The rationale for measuring a drug level must be established. The precision of technical equipment and employed methods has to be optimal. The practicability and reliability of the methods (accuracy, precision, intra- and inter-series, variability) have to be assessed, and quality-control is mandatory. A result must be interpretable. Next to analytical precision, the result has to be attributed unequivocally to a sample, which in turn had to be collected under optimal circumstances. Finally, drug monitoring has to be an integral part of individual therapy plans. In this context understanding the therapeutic range and the pharmacokinetics is essential. Competences needed to manage an entire drug monitoring program are thus many-fold. Only a multidisciplinary team appears able to provide sufficient expertise. The conditions implied in this development burden a medical office financially by needed material and personal resources.