This study evaluates the effec­tiveness and safety of mometascne furoate nasal spray (MFNS; Nason-ex®, Schering, Kenilworth, NJ) as adjunctive treatment with oral antibio­tic; amoxicillin/clavulanate potassium (ACP; Augmentin®, GlaxoSmithKline, Research Triangle Park, NC) for acute rhinosinusitis. In a double-blind, placebo-controlled study, 75 outpa­tients with moderate to severe rhin­osinusitis received ACP, 875 mg, twice daily, for 21 days with adjunc­tive twice daily MFNS 200 ng, MFNS 400 fig, or placebo nasal spray. MFNS significantly improves the symptoms of rhinosinusitis. Both doses of MFNS were well tolerated without significant treatment-related adverse events.