Air pollution is a major public health problem in the Amazon forest and in large Brazilian cities. During September of 2005, high concentrations of smoke from biomass burning were observed in the city of Rio Branco. An ecological study was conducted to evaluate the relationship between daily concentrations of particulate matter < 2.5 microm (PM2.5) and the number of respiratory disease (RD)-related emergency room visits. Daily PM2.5 concentrations exceeded recommended air quality limits on 23 days. The incidence of RDs was higher among children < 10 years of age. There was a significant positive correlation between PM2.5 concentrations and asthma emergency room visits.