During the decade of the 1980s, a wealth of information accumulated concerning automation in hematology. Recent technological advances led the way to the development of blood cell analyzers capable of performing a ten-parameter (or greater) complete blood count and five-parameter (or greater) differential leukocyte count on a small amount of whole blood and in an accurate, efficient, and economical way. The authors summarize the available information concerning the data generated by these analyzers, the mechanisms involved in the data generation, and the clinical applications and usefulness or limitations of the so-called new complete blood count parameters and of the automated differential as it compares with the manual differential.