This chapter describes the sources and pathophysiology of some potential poisons that affect birds and summarizes useful laboratory tests. The diagnosis of poisoning in birds, as in mammals, requires a complete and accurate history, careful observation of clinical signs, and a thorough necropsy evaluation. Appropriate sample handling and analysis, based on consultation with the diagnostic toxicologist, are critical (Table 19--1). Veterinary toxicology laboratories are becoming increasingly specialized, with only certain laboratories capable of analyzing for drug residues or anticoagulants, for example. Although a local laboratory may not be able to fulfill a specific test request, they may recommend an alternative laboratory or may be willing to forward the sample. As a general rule in suspect poisoning cases, large tissue samples of liver, kidney, brain, and subcutaneous fat and of crop, proventriculus, and ventriculus contents should be collected at necropsy and frozen. Appropriate samples should be submitted frozen, with the remainder held in the freezer for possible later testing. A second set of tissues should be placed in 10% formalin for histopathologic examination.