Forest fires burned near the Hoopa Valley Indian Reservation in northern California from late August until early November in 1999. The fires generated particulate matter reaching hazardous levels. We assessed the relationship between patients seeking care for six health conditions and PM(10) exposure levels during the 1999 fires and during the corresponding period in 1998 when there were no fires. Multivariate logistic regression analysis indicated that daily PM(10) levels in 1999 were significant predictors for patients seeking care for asthma, coronary artery disease and headache after controlling for potential risk factors. Stratified multivariate logistic regression models indicated that daily PM(10) levels in 1999 were significant predictors for patients seeking care for circulatory illness among residents of nearby communities and new patients, and for respiratory illness among residents of Hoopa and those of nearby communities.