This Phase I, open, randomized controlled, multiple-dose, parallel-group study investigated the potential pharmacodynamic and pharmacokinetic interactions between multiple doses of oral roflumilast and inhaled formoterol. Healthy male subjects were assigned to treatment A or treatment B. Subjects in treatment A received 500 μg/d roflumilast from day 2 to day 18 and 48 μg/d formoterol from day 12 to day 18. Subjects in treatment B received 48 μg/d formoterol from day 2 to day 18 and 500 μg/d roflumilast from day 9 to day 18. Impedance cardiography, ECG, serum potassium and glucose concentrations and effects on blood eosinophils assessed potential pharmacodynamic interactions. In addition, the safety and tolerability were evaluated. Pharmacokinetic parameters were assessed for roflumilast, roflumilast N-oxide, and formoterol.