The influence of the training, experience, and credentials of testing personnel in the increasingly complex laboratory is a significant concern. A retrospective study compared the relationship of proficiency testing (PT) performance with the credentials of the testing personnel using logistic regression analyses. Predictor variables included the practitioner's college major, degree, certification, and years of laboratory experience. There were 14,326 valid PT results and 359 practitioners of whom 245 (68.2%) had a clinical laboratory science major. Logistic regression analysis revealed that participants without a clinical laboratory science major were more likely (adjusted odds ratio, 1.849; P = .035) to produce unacceptable results compared with participants whose academic history included a clinical laboratory science program. These data suggest that clinical laboratories should be staffed by people who have completed a formal clinical laboratory education program to ensure quality of laboratory testing and to reduce the risk of medical errors.