OBJECTIVE: Indoor air pollution from the burning of such biomass fuels as wood and agricultural waste is associated with a higher risk of a number of respiratory problems. The effect on other health outcomes, such as fetal growth, has not yet been adequately documented. The objective of this study was to determine whether, among women who burn biomass fuels for cooking indoors, the use of "smoky" fires is associated with elevated hemoglobin concentration in comparison to women using "smokeless" stoves, that is, stoves that are designed to reduce indoor air pollution. This research was conducted as part of a series of preliminary studies to determine the feasibility and potential health benefits of a randomized stove intervention to reduce indoor air pollution from the burning of biomass fuels for cooking. METHODS: A cross-sectional observational study was conducted in rural highland communities of Guatemala from March to August 1994. Venous blood samples were collected and analyzed for hemoglobin and ferritin. All the women studied burned biomass fuels and cooked indoors, and none of the women was pregnant. Eighty-nine indigenous women using smokeless stoves (designated as the not-exposed group) and 185 indigenous women from the same communities using smoky fires (the exposed group) were studied. Multiple linear regression analyses were used to investigate the relationship between exposure (smokeless stove or smoky fire) and hemoglobin concentration, with adjusting for potential confounding factors. RESULTS: No effect of exposure (smokeless stove or smoky fire) on hemoglobin concentration was found in univariate or multivariate analyses. In routine post hoc analysis to determine whether hemoglobin elevation is observed in some particular subgroup, we found that the use of a smoky fire was associated with a 5.2 g/L elevation in hemoglobin concentration among women with low ferritin stores (P <0.10). CONCLUSIONS: The elevation of hemoglobin concentration through exposure to indoor air pollution resulting from the burning of biomass fuels in smoky fires for cooking could have important implications for the diagnosis of anemia. However, considering the observational nature of this study, further research using more rigorous measures of exposure to carbon monoxide as well as additional measures of iron status are needed to confirm the relationships among iron status, exposure to smoke from the burning of biomass fuels indoors, and hemoglobin concentration of women living at moderately high altitude. Further study of this matter could help to assure that appropriate adjustments to anemia cutoffs are made, if warranted, and could assist in clarifying potentially negative outcomes of exposure to smoke from biomass fuels burned indoors.