OBJECTIVE: We estimated 2,4-dichlorophenoxyacetic acid (2,4-D) exposure and systemic dose in farm family members following an application of 2,4-D on their farm. METHODS: Farm families were recruited from licensed applicators in Minnesota and South Carolina. Eligible family members collected all urine during five 24-hr intervals, 1 day before through 3 days after an application of 2,4-D. Exposure profiles were characterized with 24-hr urine 2,4-D concentrations, which then were related to potential predictors of exposure. Systemic dose was estimated using the urine collections from the application day through the third day after application. RESULTS: Median urine 2,4-D concentrations at baseline and day after application were 2.1 and 73.1 microg/L for applicators, below the limit of detection, and 1.2 microg/L for spouses, and 1.5 and 2.9 microg/L for children. The younger children (4-11 years of age) had higher median post-application concentrations than the older children (> or = 12 years of age) (6.5 vs. 1.9 microg/L). The geometric mean systemic doses (micrograms per kilogram body weight) were 2.46 (applicators), 0.8 (spouses), 0.22 (all children), 0.32 (children 4-11 years of age), and 0.12 (children > or = 12 years of age). Exposure to the spouses and children was primarily determined by direct contact with the application process and the number of acres treated. Multivariate models identified glove use, repairing equipment, and number of acres treated as predictors of exposure in the applicators. CONCLUSIONS: We observed considerable heterogeneity of 2,4-D exposure among farm family members, primarily attributable to level of contact with the application process. Awareness of this variability and the actual magnitude of exposures are important for developing exposure and risk characterizations in 2,4-D-exposed agricultural populations.