A toxicologic diagnosis is based on knowledge of the circumstances surrounding a particular case, knowledge of the clinical symptomatology, receipt and evaluation of proper specimens by a qualified laboratory, and judicious interpretation of the laboratory results. Failure to have all necessary ingredients can result in a wrong or missed diagnosis. Many veterinary toxicology laboratories can detect suspected toxicants in feed, tissue, and environmental samples at extremely low concentrations. The ability to detect toxicants at such low levels has often outpaced the ability of the diagnostician to interpret the analytic findings. This article provides guidelines for acquiring a good history, collecting appropriate samples for analysis, and selecting a veterinary analytic laboratory to maximize the probability of making a correct toxicologic diagnosis.