ABSTRACT Assessment of the true impact al pharmacists' interventions in pharmaceutical care is crucial to the justification of investment in resources for clinical pharmacy services. In a large study of clinical pharmacy interventions in hospitals, intervening pharmacists and attending physicians assessed the impact of the intervention on three aspects: therapeutic benefit, risks, and drug costs. The study showed that hospitals providing the highest level at pharmacotherapy monitoring made more interventions per patient and that, in these institutions, the impact was greater on therapeutic benefit and risk reduction. Both pharmacists and physicians caring for the patient had assessed the impact. It was deemed important to validate these results. External panels of academic clinical pharmacists and clinical pharmacology physicians were chosen to review a sampling of cases to determine their level of agreement with their professional colleague (pharmacist or physician) at the original site. Differences were found in the assessments for both the pharmacist panel reviewing the site pharmacists and the physician panel reviewing the site physicians. In general, the review panels tended to be less positive about therapeutic benefit and risk reduction, but similar about the impact on drug costs. Although validation exercises are desirable in such research, it remains to be established whether the expert panel approach is preferred to other methods such as the more arduous measurements of health outcomes, or even the subjective impression of the physician and pharmacist involved with the care of that patient.