INTRODUCTION: Euphorbium compositum SN (Biologische Heilmittel Heel GmbH, Baden-Baden, Germany, a homeopathic combination preparation available in form of drops, nasal spray, and injection solution), is prescribed for inflammation of the mucosae of the nose and sinuses. Infections in these areas are primarily of viral origin although bacterial superinfections are also common. OBJECTIVE: The main question was whether or not this homeopathic remedy shows an activity against viruses responsible for infections of the respiratory tract. METHODS:This in vitro study using virus plaque reduction assays examined the effect of Euphorbium compositum SN against pathogens causing various viral infections: influenza A virus, respiratory syncytial virus (RSV), human rhinovirus (HRV) and herpes simplex virus type 1 (HSV-1). RESULTS: Analysis of virus production after treatment of the infected cells with the remedy showed an antiviral activity of Euphorbium compositum SN against RSV and HSV-1. In addition, an antiviral effect against influenza A virus and HRV, though minimal, was, also noted. Analyses of the plant-derived components of Euphorbium compositum SN, e.g. Euphorbium resinifera, Pulsatilla pratensis and Luffa operculata for their antiviral activity revealed a clear activity of Euphorbium resinifera and Pulsatilla pratensis against RSV. In contrast, no effect was detected using the same protocol with Luffa operculata. CONCLUSIONS: Euphorbium resinifera and Pulsatilla pratensis as components of Euphorbium compositum SN are responsible for its antiviral activity. Copyright 2001 S. Karger GmbH, Freiburg