Abstract: On the morning of January 19, 1994, a diesel truck was left running while employees were unloading mail at the rear dock of Loves Park Branch Post Office. Over the course of 2 hours, Employees #1 through #23, in the clerk and carrier handling areas, developed headaches, nausea, and eye/nose irritation. No attempt was made to evacuate the building, but the local fire department was summoned. The firemen set up ventilation and called for paramedics. Four ambulances responded, providing oxygen treatment to those employees feeling the worst, and taking them to one of three hospitals. Two employee-driven vans transported the remainder of the ill employees. All employees received at least a 1/2 hour of oxygen therapy at the hospitals, and most were tested for carboxyhemoglobin blood levels. All levels were found to be normal. Many employees experienced headaches for the rest of the day and were given the option to go home.