This is a Phase I, three period, two sequence, open-label, randomized, crossover study, with the primary objective of testing the safety and tolerability of combined oral doses of theophylline and bambuterol in healthy human subjects. The secondary objective is to assess the pharmacokinetic profiles of theophylline and bambuterol when administered alone or in combination. It is hypothesized that the combination of these drugs is generally safe, and that no drug interaction can be observed.