Background: Nearly half of the world's population is exposed to household air pollution (HAP) due to long hours spent in close proximity to biomass-fueled fires. Objective: We compare CO exposures and concentrations among study promoted intervention stove users and control stove users in San Marcos Province, Cajamarca region, Peru. Methods: Passive CO diffusion tubes were deployed over a 48-hour sampling period to measure kitchen CO concentrations and personal mother and child CO exposures in 197 control and 182 intervention households. Results: Geometric means (95% CI) for child, mother, and kitchen measurements were 1.1 (0.9-1.2), 1.4 (1.3-1.6), and 7.3 (6.4-8.3) ppm in control households, and 1.0 (0.9-1.1), 1.4 (1.3-1.6), and 7.3 (6.4-8.2) ppm among intervention households, respectively. Conclusion: With no significant differences between control and intervention CO measurements, results suggest that intervention stove maintenance may be necessary for long-term reductions in CO exposures. © W. S. Maney & Son Ltd 2013.