Genetic risk factors are a critical component of many epidemiologic studies; however, concerns about genetic research might affect participants' willingness to enroll. The authors assessed factors associated with completion of mailed buccal-cell collection kits following telephone interviews at the Atlanta, Georgia, study site of the National Birth Defects Prevention Study. Pregnant women who were interviewed after June 30, 1999, and had an estimated delivery date of December 31, 2002, or earlier were included (n = 1,606). For this time period, overall interview participation was 71.9%. Among those interviewed, 47.6% completed the buccal-cell collection kit (61.1% of non-Hispanic Whites, 34.9% of non-Hispanic Blacks, and 39.1% of Hispanics). Non-Hispanic White race/ethnicity, an English-language (vs. Spanish) interview, receipt of a redesigned mailing packet and an additional $20 incentive, and consumption of folic acid were associated with higher buccal-cell kit participation. Among non-Hispanic White mothers, higher education, intending to become pregnant, and having a child with a birth defect were associated with increased participation. Among non-Hispanic Black mothers, receipt of the redesigned packet and $20 incentive was associated with increased participation. Among Hispanic mothers, an English-language interview, higher education, and receipt of the redesigned packet and $20 incentive were associated with increased participation. At this study site, minority groups were less likely to participate in DNA collection. Factors associated with participation varied by race/ethnicity.