Urinary methoxyphenols have been proposed as biomarkers for woodsmoke exposure, but few field studies have been undertaken. We evaluated these biomarkers for assessing the exposure to woodsmoke of householders in rural Guatemala. The study population was a subset (10 female cooks, 2 female non-cooks, and 8 male non-cooks ranging in age from 7 to 60) drawn from those participating in a longterm randomized intervention trial (RESPIRE) in the highlands. All households rely solely on woodburning for cooking and home heating. Approximately half of the homes in the trial used open woodfires in the home, while the intervention group used cookstoves, called "planchas, "that vent most of the woodsmoke outdoors through a chimney. Corrected for creatinine levels, 16 of the 19 methoxyphenols measured were lower in the urine of cooks using the plancha; and 11 of the 19 compounds were lower in the urine of non-cooks from homes using the plancha. Furthermore, the 4 low-molecular-weight syringyl methoxyphenols (syringol, methysyringol, ethylsyringol, propylsyringol) were each moderately correlated (r2 = 0.71,0.64, 0.68, 0.53 respectively, with all p < 0.05) with personal exposure measurements determined by carbon monoxide (CO) passive diffusion tubes, but not with CO in exhaled breath. 48-Hour kitchen area measurements of PM2.5 mass, PM2.5 levoglucosan, and CO were highly correlated (>0.89) with each other and moderately correlated (0.54-0.78) with personal CO measurements. Although based on relatively few measurements, this study demonstrates that the urinary concentrations of specific methoxyphenols may be effective biomarkers of short-term exposures to inhaled woodsmoke in field conditions.