Method for preparing a practically anhydrous tiotropium bromide micronizate (A) comprises comminuting crystalline tiotropium bromide monohydrate (I) in a gas-jet mill in which the particles are comminuted in a fluidized powder bed. An independent claim is included for (A) produced by the new method. ACTIVITY : Antiasthmatic. No details of tests for antiasthmatic activity are given. MECHANISM OF ACTION : Anticholinergic.