An experiment with adult humans investigated the effects of response-contingent money loss (response-cost punishment) on monetary-reinforced responding. A yoked-control procedure was used to separate the effects on responding of the response-cost contingency from the effects of reduced reinforcement density. Eight adults pressed buttons for money on a three-component multiple reinforcement schedule. During baseline, responding in all components produced money gains according to a random-interval 20-s schedule. During punishment conditions, responding during the punishment component conjointly produced money losses according to a random-interval schedule. The value of the response-cost schedule was manipulated across conditions to systematically evaluate the effects on responding of response-cost frequency. Participants were assigned to one of two yoked-control conditions. For participants in the Yoked Punishment group, during punishment conditions money losses were delivered in the yoked component response-independently at the same intervals that money losses were produced in the punishment component. For participants in the Yoked Reinforcement group, responding in the yoked component produced the same net earnings as produced in the punishment component. In 6 of 8 participants, contingent response cost selectively decreased response rates in the punishment component and the magnitude of the decrease was directly related to the punishment schedule value. Under punishment conditions, for participants in the Yoked Punishment group response rates in the yoked component also decreased, but the decrease was less than that observed in the punishment component, whereas for participants in the Yoked Reinforcement group response rates in the yoked component remained similar to rates in the no-punishment component. These results provide further evidence that contingent response cost functions similarly to noxious punishers in that it appears to suppress responding apart from its effects on reinforcement density. (Contains 7 figures and 3 tables.)