This study assessed differences in response rates to a mailed health survey by adults in two neighboring rural midwestern counties with differential incentives, of dollar 2.00 and dollar 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 dollar 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 S2 incentive. The response rates were 71% using the dollar 2 incentive and 73% using the dollar 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 dollar 2.00 rather than dollar 5.00 incentive, a cost per returned survey of dollar 5.24 versus dollar 9.13, respectively. The findings support Dillman's principle of diminishing returns as the size of the incentive goes up.