This study assessed the acceptability of collecting hair from Latino children to measure environmental tobacco smoke (ETS) exposure and examined the concurrent validity between nicotine and cotinine levels in children's hair in relation to adult reports of the children's ETS exposure. Trained Latina lay community health advisors recruited 143 Spanish-speaking Latino adult volunteers and their children. Bilingual-bicultural measurement technicians collected two types of data: (a) the adult's paper-and-pencil report about the child's past-month exposure to cigarettes in the home and car and (b) a sample of the child's hair to be analyzed for nicotine and cotinine. Of the eligible subjects, 8.5% declined to participate because of the hair collection protocol, some citing cultural beliefs. Among participants in the study, few problems arose related to hair collected, probably because of the culturally sensitive approach used during recruitment and measurement. Adults' reports of exposure, hair nicotine, and hair cotinine showed considerable variation and were skewed to the right. Average nicotine levels for these children appeared to be comparable to those reported elsewhere, whereas cotinine levels appeared to be somewhat lower. Hair nicotine was more detectable than hair cotinine and, compared with cotinine, showed a clearer linear relationship with adults' reports. However, associations between adults' reports and both biological measures were modest. Collecting hair samples in the field (i.e., participants' homes) to measure Latino children's ETS exposure is generally acceptable when appropriate methods are used. Hair nicotine may be a more valid and practical biological measure than hair cotinine. Hair sampling may be a potentially useful, noninvasive technique in ETS studies, although the modest associations of constituents in children's hair with adults' reports indicates that each measure provides different information about ETS exposure.