The objective of data quality assurance procedures in clinical studies is to reduce the number of data errors that appear on the data record to a level which is acceptable and compatible with the ultimate use of the recorded information. A semi-automatic procedure has been developed to detect and correct data entry errors in a study of the feasibility and efficacy of home health monitoring for patients with cystic fibrosis. Daily self-measurements are recorded in a diary, mailed to the study coordinating center weekly, and entered into the study's INSIGHT clinical database. A statistical error detection test has been combined with manual error correction to provide a satisfactory, reasonable cost procedure for such a program. Approximately 76% of the errors from a test diary entry period were detected and corrected by this method. Those errors not detected were within an acceptable range so as no to impact the clinical decisions derived from this data. A completely manual method detected 88% of all errors, but the review and correction process was four times more costly, based on the time needed to conduct each procedure.