Three experiments are reported which investigated the effects of cost (point loss per response) upon human-observer responses maintained by VI and FI schedules of reinforcement (acquisition of points via critical-signal detections). (I) Cost attenuated VI response rates without substantially disturbing the constancy of responding, regardless of the presentation sequence of the no-cost and cost conditions. (II) FI scalloping appeared only under cost conditions. Under no cost, a constant rate of responding (similar to VI performance) characterized inter-reinforcement intervals. Exposure to cost did not prevent the recovery of previously established no-cost baselines. (III) FI irregularities, analogous to those commonly observed under FI reinforcement schedules, may be produced by different temporal presentations of the no-cost and cost conditions. The results of all three experiments emphasize the importance of cost as a factor in the maintenance of human behavior on schedules of positive reinforcement.