The frequency, position, and type of errors were analyzed for sequence data which were generated with the help of (I) a manual digitizer, (II) an off-line automated film reader, and (III) an on-line automated gel reader. About 400 film/gel readings were analyzed and the results were used to generate error profiles for each method. The profiles identify several method- and project-specific problem areas and provide useful guidance for the assessment of DNA sequence data in general.