Five cigarette smoking methadone maintenance patients (MMP) participated in a within-subjects (A-B-A-B) study involving repeated application of carbon monoxide (CO)-contingent payments for reductions in smoke intake. To replicate and extend findings from an earlier study in non-drug-abusing smokers (Stitzer & Bigelow, 1982), we used the same contingent reinforcement procedure that involved the delivery of a monetary payment ($5) for CO readings which were 50% or less than the average value of readings obtained during the prior noncontingency period. Although four of the five subjects earned the contingent payment on at least three of the eight occasions, the overall effect of the intervention on CO level was nonsignificant. Daily smoking records revealed significantly lower rates during the first contingency intervention for the group as a whole. Significant correlations between CO and the time interval since smoking prior to CO measurement were found. The rather modest intervention effects suggest that important parameters be considered when designing contingency management procedures to reduce cigarette smoking in this difficult population of drug abusers.