Sixty-day-old, male and female rats were exposed by inhalation to fog oil smoke. Mortality, LC50, subacute and subchronic studies were performed. Mortality studies showed fog oil smoke to be 100% lethal at 11.0 mg/L, 95% lethal at 5.0 mg/L, 20% lethal at 1.0 mg/L and 0% lethal at 0.1 mg/L after a 6-hour exposure. The observed LC50 of fog oil smoke after a 3.5-hr exposure was 5.2 mg/L. In the subacute and subchronic studies, rats were exposed to air, 0.2-, 0.5-, or 1.5-mg/L fog oil smoke for 3.5 hr/day, 4 days/wk for either 4 of 13 wk. Both pulmonary and systemic effects were investigated one day after the exposure ceased. For one 13-wk exposure group, animals were also examined 4 wk after the exposure. Following the srbacute 4-exposure to 1.5 mg/L, a multifocal pneumonitis was observed. Lung lavage had an elevated number of polymorphonuclear leukoctes (PMNs), alveolar macrophages and lung weights was observed after exposure to 0.5 mg/L. Pulmonary function tests revealed an increase in end expiratory volume (EEV) after 1.5mg/L. Systemic effects after the subacute exposure were minimal. A decrease in zoxazolamine-induced paralysis time was observed following both 0.5 and 1.5 mg/L; however, no effect on pentobarbital-induced sleeping time was observed. Behavioral studies were negative, as were clinical chemistries and immune function tests.