The effects on response rates to mail surveys of prepayment cash incentives, charitable donations, and the chance to win a lottery prize are examined in a true experimental design. A survey on environmental issues was conducted during the fall of 1994 among 3,088 households drawn from the Grand River watershed region of southwestern Ontario, Canada. The 20-cell incentives experiment crossed three levels of prepaid monetary cash incentive ($2, $5, and $10) with a control group (no cash incentive), plus the offer to make a charitable donation ranging from $2 to $10 on behalf of the respondent, or participation in a lottery for prizes of $200. The overall response rate to the survey, with three follow-ups, was 70.7 percent with the effects of the prepaid cash rewards demonstrated, but not those for the lottery or charitable donations. Logistic regression analysis of response rate supports a main effects model for cash incentives but does not support either of two alternative models for main effects of the lottery and charitable donations or interactions. Further analysis demonstrates a pattern of earlier response as a result of prepaid incentives. The findings are discussed in terms of their cost-benefit implications and with respect to conceptualizations of respondents' motives for completing mail questionnaires.