The uses and advantages of a digital computer system in medical research were explored in a pilot study of 138 records from an outpatient clinic. Information was coded with the help of the Standard Nomenclature of Diseases and Operations, the Cornell Medical Index, and other aids, and it was found possible to punch a history of 195 questions on International Business Machine cards in 40 seconds. Manual punching can be avoided by a procedure (mark-sensing) whereby information recorded on blanks by electrographic lead pencils can be transferred directly to punch cards by machine. Data in this form can be stored easily and retrieved quickly. The study demonstrated the possibility of locating rapidly, in a very large collection of records, a group of charts meeting any desired combination of requirements.