This study provides data on differences between respondents and nonrespondents by gender and ethnicity in a multicenter community-based study that is rarely collected and that may be useful for estimating bias in prevalence estimates in other studies. Demographic, general health, and cardiovascular risk factors were examined in black and white respondents and nonrespondents to the Atherosclerosis Risk in Communities (ARIC) Study, a prospective study investigating cardiovascular risk factors in approximately 16,000 adults that was initiated in 1986 in four U.S. communities. In one of the communities (Jackson, MS) black participants were recruited exclusively; in another (Forsyth County, NC) 12% of the eligible sample were black, whereas the samples in Washington County, MD and the northwestern suburbs of Minneapolis, MN were almost all white. Demographic and health characteristics were collected during a home interview. Subjects who subsequently agreed to complete a clinical examination were defined as respondents, while eligible participants who only took part in the home interview were considered to be nonrespondents. Approximately 75% of age-eligible individuals (45-64 years) in each community completed the home interview. In three of the communities 86-88% of those who took part in the home interview also completed the clinic examination, whereas only 65% did so in Jackson. Among white participants, response rates were similar in men and women and between communities. Among black participants, the response rates were considerably lower, particularly in men. White male respondents reported a higher socioeconomic status, better general health and a lower prevalence of cardiovascular disease and associated risk factors than white male nonrespondents. The difference between white respondents and nonrespondents were greater for men than women despite similar response rates. Among black participants, respondent/nonrespondent difference were usually of smaller magnitude or absent, particularly in women. General health status and recent hospitalization rates were almost identical in black respondents and nonrespondents. Low response rates can bias estimates of prevalence in community-based studies although differences between respondents and nonrespondents tend to exaggerate real differences between respondents and the eligible population sampled. For example, among white males 25% of respondents and 44% of nonrespondents were current smokers, yet the estimated community prevalence of smoking was 31%. In conclusion, difference observed between respondents and nonrespondents were in the expected direction, but were greater for men than women and for whites than blacks.