A survey of all licensed medical laboratories performing activated partial thromboplastin time (aPTT) testing in Canada was undertaken; the response rate was 50.7%. Preanalytic phase of testing seemed generally satisfactory, although 46% of laboratories were still using 3.8% or a 129-mmol/L concentration of citrate, and only 59% of institutions routinely performed testing to verify the platelet-poor status of the plasma used for aPTT testing. There were also concerns relating to the speed and duration of centrifugation for specimen preparation. While more than 67% of institutions had established an individual therapeutic range for aPTT testing, only 47% of laboratories verified this range with heparinized samples. Approximately 67% of the institutions that had verified the range had done this by spiking heparin concentrations into pooled plasma rather than using ex vivo specimens from patients receiving heparin therapy. There seemed to be a need for increased education about circumstances under which the therapeutic range should be rechecked and current standards for screening for the lupus anticoagulant. More than 71% of Canadian institutions surveyed used low-molecular-weight heparin, which may obviate many of the issues surrounding aPTT testing. Overall performance as documented by survey results seemed similar to that reported for the United States and Australasia.