The extent of inhalation exposure to loggers from two-stroke chain saws was measured and evaluated under various conditions. Carbon monoxide, measured by personal air monitoring and determination of carboxyhemoglobin levels of the loggers, was used as an indicator of exhaust exposure. Video recordings were made to analyze the influence of varying working conditions and the individual handling of the chain saw on the amount of pollutants inhaled. The American Conference of Governmental Industrial Hygienists biological exposure index (BEI) for carboxyhemoglobin (3.5%) was exceeded during logging in heavy timber stands. When workers were paid on a piecework basis, carboxyhemoglobinemia increased to its maximum level in the first 2-3 hours of the shift and then declined. After 8 hours carboxyhemoglobin levels were 20-30% lower compared with the maximum. Increased exhaust inhalation with short-term exposures to carbon monoxide up to 400 ppm was observed in the following conditions: (1) felling operations, (2) other operations performed in a leaning of squatting position, (3) limbing in thick tops of coniferous trees, (4) working at low wind velocity, and (5) working in thick forest stands. Maximum allowable blood concentrations for carboxyhemoglobin are exceeded in chain saw operators in logging operations. Blood sampling at the end of the workday is not always suitable for determining the highest carboxyhemoglobin levels in loggers during the shift. The exposure of chain saw operators to exhaust increases under certain conditions.