A flow-injection turbidimetric procedure exploiting merging zones is proposed for determining homatropine methylbromide (HMB) in pharmaceutical preparations. The determination is based on the precipitation reaction of homatropine methylbromide with silicotungstic acid in acidic medium to form a precipitate, which was measured at 410 nm. The analytical curve was linear in the HMB concentration range from 8.1 x 10(-5) to 2.2 x 10(-4)mol l(-1), with a detection limit of 5.0 x 10(-6)mol l(-1). The recoveries ranged from 96 to 103%, the sampling frequency was 70 determinations per hour and relative standard deviations were less than 1.5% (n=10). The results obtained for commercial formulations using the FIA procedure were in good agreement with those obtained by using a comparative method.