Results of many routine laboratory assays supply important diagnostic information and are an important part of patient care in many situations. Ensuring the accuracy of these results is not only important from a diagnostic standpoint but can prevent the frustration inherent when the effort of collecting and submitting samples does not yield interpretable results. This article discusses some of the routinely encountered problems (and how to avoid them) associated with performing the more commonly requested tests: complete blood cell counts, chemistry profiles, coagulation testing, and cytology specimens. The article presents a general discussion of sample collection and handling and then some specific considerations for the handling of the previously mentioned tests.