This is a randomized, double-blind, placebo-controlled, crossover, single center study of SCH 619734 in subjects with chronic cough from an unknown cause. Subjects will be randomized to receive SCH 619734 or placebo for 7 days with 7 days' follow-up. After a 6 week washout period, subjects will be crossed over to the other treatment. The primary objective is to evaluate the effectiveness of SCH 619734 in reducing cough reflex sensitivity as determined by a challenge with capsaicin, an agent that induces cough.