The purpose of this paper is to determine whether giving a monetary incentive has an effect on reported drug use rates. Sampling weights were adjusted to account for the differential response rates between the incentive and non-incentive cases. Then logistic regression models of substance use were fitted as a function of the incentive level (0,20, and $40) while controlling on other variables that might mask the relationship. The incentive had a statistically significant effect on the reported past-year use of marijuana and on past-month use of cocaine, but no effect on past-month or lifetime use of marijuana. Offering a monetary incentive to respond can result in different estimated prevalence rates for the incentive and non-incentive groups. The extent of the difference may be a function of the perceived level of social disapproval of the substance and the reference period (past month, past year, or any past use). Some of the difference appears to be due to differences in substance use rates between the group that had traditionally reported without an incentive and the new group attracted by the incentive. Other differences appear to result from more honest reporting among the traditional respondents.