The activated clotting time (ACT) is commonly used in veterinary medicine as an assessment of dysfunction within the intrinsic clotting cascade. Performing the test requires little techincal expertise and no special equipment except for a heating block or constant temperature waterbath, neither of which is routinely found in veterinary practices. The purpose of this study was to determine whether performing the test using a human axilla as the heat source was accurate for both normal dogs and clinically ill dogs (with prolonged ACT's) when compared to using a heating block as the head source. The results of this study reveal that the axillary method of ACT determination has acceptable clinical agreement with the heating block method. Thus, the axillary method of ACT determination is an acceptable alternative when no constant temperature heating source is available.