Electronic medical records (EMRs) hold the promise of making routine comprehensive measurement of care quality a reality. However, there are many informatics challenges that stand in the way of this goal. Guidelines are rarely stated in precise enough language for automated measurement of clinical practices and the data necessary for that measurement often reside in the text notes of EMRs. We designed a technology platform for scalable and routine measurement of care quality using comprehensive EMR data, including providers' freetext notes documenting clinical encounters. We are in the process of implementing this system to assess the quality of ambulatory asthma care in two diverse healthcare systems: a mid-size HMO and a consortium of Federally Qualified Healthcare Center (FQHC) clinics on the west coast of the United States.