Cotton workers are recognized as being at risk of developing occupational lung diseases. Some researchers have identified endotoxins as being a potential etiologic agent for some of the respiratory problems. This study wants to document the concentration of endotoxins found in the ambient air of textile mills where cotton fibers are handled and to identify the processing steps where the highest endotoxins concentrations in the air were found and the one where the relative limit values (RLVs) are exceeded. The 4 mills studied process cotton fibers. All the air samples were analyzed using the chromogenic Limulus Amoebocytes lysate LAL method using a kinetic detection principle based on the IRSST's standard method. In this study, a large variability in the concentrations of endotoxins in the air was observed, depending on the mill, the processing step, and the time. Despite these variations, some processes can be identified as being major generators of endotoxins in the ambient air of the mills. The highest concentrations were measured in the weaving and drawing processes and reached 10,000 EU m(-3) of air. The opening, cleaning, carding, spinning and drawing processes are the other major endotoxins generating processes with concentrations from 24 to 8,700 EU m(-3) of air. The endotoxins concentrations exceeded the RLVs for 55% of the workstations in this project. This study demonstrated that endotoxins levels in the cotton industry are high and appropriate control measures are needed.