This study assessed differences in response rates to a mailed health survey by adults in two neighboring rural midwestern counties with differential incentives, of $2.00 and $5.00. Potential respondents in each county were randomly selected from a commercial database of residents' addresses. County “F” respondents ( n = 541) which were 57% female and 95% Euro-American having a mean age of 47.3 yr. ( SD = 16.9), received the $5 incentive. County “H” respondents ( n = 514) were 63% female, 95% Euro-American, had a mean age of 49.0 yr. ( SD = 14.7), and received a $2 incentive. The response rates were 71% using the $2 incentive and 73% using the $5 incentive. These were not significantly different by chi-square test. The more cost-effective incentive for increasing the response rate of adults in this rural midwestern sample was to code the envelopes and use a $2.00 rather than $5.00 incentive, a cost per returned survey of $5.24 versus $9.13, respectively. The findings support Dillman's principle of diminishing returns as the size of the incentive goes up.