The study will examine which dose of YM178 is best in terms of efficacy, safety and tolerability compared to placebo and compared to tolterodine, a marketed product.

Inclusion Criteria:

• Patients over 18 years suffering from overactive bladder (OAB) for more than 3 months

Exclusion Criteria:

• Pregnant and breastfeeding women
• Any medical condition or need for co-medication which interferes with the drug under investigation (YM178) or the comparator (tolterodine)