General aspects of avian clinical pathology are reviewed. It is concluded that in a clinical setting a volume of blood equivalent to 1 per cent of body weight can be collected safely from avian species for laboratory examinations. The anticoagulant of choice for most laboratory investigations is lithium heparin. In most bird species the right jugular vein is the preferred site for routine blood sampling. The use of a vacuum system greatly facilitates the procedure. The importance of immediately processing blood samples is explained. The many variables that may influence haematological or biochemical parameters are discussed and the reasons for determining blood chemical reference values by non‐parametric methods are emphasised.