The differential leukocyte counts performed by an automated hematology analyzer, the Technicon H‐1E Hematology System, and traditional microscopic method (M‐Diff) from blood samples of 129 horses, 40 cattle, and 140 cats were compared. The comparison was repeated after selected subsets of data were created by deleting samples with certain patterns suggesting error with the automated differential cell count (A‐Diff). The two methods had good comparison of results for neutrophils and lymphocytes in all three species. Results for equine monocytes correlated moderately well between the two methods and the correlation improved in the selected data set. Monocyte results did not compare well for the bovine and feline samples. The A‐Diff for feline eosinophils was inaccurate. The A‐Diff may be accurate for bovine and equine eosinophils but too few examples of eosinophilia were present in the sample set to prove this. Basophils were too rarely seen in cattle and horses to validate A‐Diff accuracy, but basophilia identified by the M‐Diff in a cat was not identified