In a monocenter, placebo-controlled, double-blind, parallel-group study, 20 patients with acute symptoms of rhinosinusitis were treated with either fusafungine (CAS 1393-87-9, Locabiosol Dosier-Spray) (n = 10) or placebo nasal spray (n = 10). One patient from the placebo group was withdrawn from the study on the day of inclusion for noncompliance reasons. At the beginning of the 2-week treatment period, absence of an acute exacerbation of sinusitis with, e.g., opacity or fluid in any of the sinuses, was documented by computed tomography. Efficacy of treatment was assessed using objective measurements (e.g. sonography, rhinomanometry, acoustic rhinometry, and endoscopy) as well as scores recorded by the investigator on 6 consecutive visits before and after 1, 3, 7, 10, and 14 days of treatment, and by the patients on a diary card. Drug safety was evaluated on the basis of twice-daily assessment of general well-being and side effects. Statistical analysis of the data evidenced a positive effect of fusafungine as early as by the first 24 h of treatment (reduction of symptom score D0-->D1: p < 0.01), which was not seen in the placebo group (p = 0.2174). In the final assessment, both investigator and patients rated global efficacy better with fusafungine. In some instances, the intergroup difference achieved statistical significance (patient diaries, p = 0.0342). Side effects such as reactions at the application site mainly occurred in patients in the placebo group, who rated tolerability markedly worse than patients taking fusafungine (p = 0.0304; patient diaries, p = 0.0170).