An increased prevalence of respiratory problems among softwood lumber mill workers has been observed in a number of studies. These workers are potentially exposed to a variety of respiratory hazards including wood dust, abietic or other resin acids, monoterpenes, and fungi, as well as endotoxins. The objectives of this study were to determine if lumber mill workers were exposed to hazardous levels of airborne endotoxin and to identify the factors contributing to high exposures. Personal endotoxin samples (n = 216) were collected in four lumber mills in the Canadian province of British Columbia. The mean personal exposure concentration was 2.09 ng/m.(3) and 9% of the samples were above 5 ng/m.(3). Factors related to the personal endotoxin exposure were type of job, use of compressed air, the percentage of time spent in a booth or cab during a shift, and dust concentration. Log storage practices were also suspected of playing a role. The levels of exposure observed in this study were low compared to the levels reported for populations with respiratory problems attributed to endotoxins.