The goal was to describe the change in the rate of epinephrine dosing errors in the treatment of pediatric patients in prehospital cardiopulmonary arrest after the Los Angeles County Emergency Medical Services Agency instituted a program in which paramedics were required to use the Broselow tape and to report color zone categories to the base station and base stations were given and instructed formally in the use of the color-coded drug dosing chart. An observational analysis of a natural experiment was performed. Children < or = 12 years of age who were determined to be in prehospital cardiopulmonary arrest and who received prehospital epinephrine treatment by paramedics, in the periods of 1994 to 1997 and 2003 to 2004, were included in the study. In the 1994 to 1997 cohort, we identified 104 subjects in prehospital cardiopulmonary arrest who received epinephrine with a documented weight and route of administration. Only 29 of 104 subjects in the 1994 to 1997 cohort received the correct dose, whereas 46 of 104 subjects received a first dose within 20% of the correct dose. In the 2003 to 2004 cohort, we identified 41 children < or = 12 years of age who were in cardiopulmonary arrest and received prehospital epinephrine treatment but 4 children were excluded, leaving 37 subjects. Twenty-one of 37 subjects received the correct dose, whereas 24 of 37 subjects received a dose within 20%. The odds ratio for obtaining the correct epinephrine dose after the system changes versus before was 3.0, and that for obtaining a dose within 20% of the correct dose was 2.5. The program seems to have resulted in reduction of the rate of epinephrine dosing errors in the prehospital treatment of children in cardiopulmonary arrest in Los Angeles County.