To the Editor. — In their article Changing Patterns of Asthma Hospitalization Among Children: 1979 to Gergen and Weiss1state that simply reclassifying bronchitis to asthma cannot fully explain the increase in asthma hospitalizations. From 1979 to 1987, hospitalization for pneumonia (International Classification of Diseases, Version 9, Clinical Modificationcodes 480 through 486) dropped by 51 000, while asthma (International Classification of Diseases, Version 9, Clinical Modificationcode 493) hospitalizations increased by 50 000.2The trend started in 1980 and continues. Thus, a diagnostic shift from pneumonia to asthma could account for the entire increase in asthma hospitalization during this period. In 1988, pneumonia hospitalizations decreased by 19 000 and asthma hospitalizations increased by 15 000 (Jean Kozak, RN, MA, National Center for Health Statistics, written communication, April 12, 1990). I believe that diagnostic transfer from pneumonia plays a major but little-noticed role in changes in hospitalization rates.