OBJECTIVES: This study evaluated the effectiveness of smoking restrictions. METHODS: We measured particulate concentrations in restaurants with different levels of allowable smoking. RESULTS: Mean particulate concentrations were 70% higher in establishments without smoking restrictions compared with those with partial smoking restrictions. Concentrations in nonsmoking restaurants were reduced by an additional 20% to 30%. Measurements of cadmium, an environmental tobacco smoke (ETS) marker, implicated ETS as the major source of particulate in restaurants that allowed smoking. CONCLUSIONS: Partial smoking restrictions substantially reduce, but do not eliminate, ETS exposure in restaurants. Occupants of nonsmoking restaurants avoid ETS exposure but may experience substantial particulate exposures from cooking emissions.