In a comprehensive drug surveillance system that monitored consecutive hospitalized medical patients who received propoxyphene hydrochloride for mild or moderate pain, or for headache, the drug was rated ineffective by the attending physicians in 10.1 % of 335 nonsmokers, 15.0% of 347 patients who smoked 20 cigarettes per day or less, and 20.3% of 153 patients who smoked more than 20 cigarettes per day (p < 0.01). There was a linear increase in the proportion of ineffective ratings of about 5% for each pack of 20 cigarettes smoked per day (p < 0.005).