Background and objective: a previous study in Bucaramanga showed no association with the presence of respiratory symptoms in children under seven years and two areas of different outdoor air pollution. Hypothesis if the presence of biological contaminants intra household is positively associated with respiratory symptoms consistent with bronchial asthma in children under seven years, of pollution extradomiciliary independent. Methods: cross sectional analytic, less than seven years living in two areas of the city of different levels of air pollution by particulate matter respirable, fraction less than 10 microns. We assessed respiratory symptoms consistent with asthma the questionnaire ISAAC and EILS validated in Spanish; application questionnaire and measurements of indoor air biological pollutants samples were collected by standardized laboratory methods and use log binomial regression model for multivariate analysis, it allowed to evaluate associations by estimate prevalence ratios. Study funded by the University Industrial of Santander. Results: 678 children, mean age 42 months. The prevalence of symptoms indicative of Asthma was 8,0%; (95% CI: 5,6 – 9,6), without significant differences between the two outdoor pollution areas of the city. Binomial model analysis showed that four variables consistent (acremonium, pneumonia, prematurity and presence of pets at home) and related to the presence of respiratory symptoms consistent with asthma. The presence of pets in the home has an inverse relationship. Conclussion: the intramural exposure to biological contaminants (dust mites and fungi), history of prematurity, pneumonia, rhinitis and family history of asthma increases the probability of occurrence of symptoms suggestive of asthma in this population. The presence of pets could be a protective factor.