This trial compares the outcome of treatment of mild to moderate asthma: inhaled tiotropium bromide versus placebo.

Inclusion Criteria:

• Informed consent
• Male or female, at least 18 years old
• Documented medical history of asthma (diagnosis at least 6 months ago)
• Non-smoker or at least stopped for 1 year (in case smoked earlier: maximum of 10 pack-years)
• Able to conduct a technically acceptable spirometry, methacholine and neurokinin-A provocation test.
• At visit 1: PC20 methacholine ≤ 8 mg/ml AND ≤ 3.3x10-7 mol/ml for the neurokinin-A provocation test.
• At visit 1: forced expiratory value in one second >= 80% of the predicted value.
• Female subjects may not get pregnant and should be using adequate contraception.

Exclusion Criteria:

• Airway infection within 6 weeks prior to first study visit.
• Other respiratory diseases (eg COPD, lung cancer, etc.)
• Participating in another clinical trial.
• Clinically relevant systemic diseases, other than asthma.
• Clinically significant laboratory deviations.
• Alcohol or drug abuse.
• Female subjects who are lactating.