Abstract During a 4-week period in late November and early December 1992, blood samples from individuals exposed to auto emissions derived from oxyfuel were analyzed. Effects on the immune system were measured by monitoring plasma interleukin 6 (IL-6) levels in a total of 22 subjects at the beginning and the end of the workday. After ∼ 8 h of workplace exposure, mean levels of IL-6 of 2.5 pg/ml were obtained. While some subjects showed increasing levels at the end of the workday, there was no difference between morning and evening IL-6 means. Our conclusion is that single day exposures to oxyfuel and its combustion products does not show an immediate effect on the immune system as judged by serum IL-6 levels.