Two continuous performance tests were administered to normal adult subjects. The mode of presentation (visual or auditory) and the type of task (vigilance or distractibility) were varied, and their effects on performance measured. Data were collected on eighty-two subjects, and results indicated that auditory presentation of stimuli increased the difficulty of both tasks. Results also suggest that the distractibility task administered in either mode was more difficult than the vigilance task. Intercorrelations among the four continuous performance tasks are provided. Normative data are presented on all four tasks administered. A measure of symptoms of attention-deficit disorder in adults, the Adult Behavior Checklist, was found to correlate significantly with another measure of pathology, the SCL-90-R.