Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Context: Medicinal plants are well known for their use in traditional folk medicine as treatments for many diseases including infectious diseases. Objective: Six Brazilian medicinal plant species were subjected to an antiviral screening bioassay to investigate and evaluate their biological activities against five viruses: bovine herpesvirus type 5 (BHV-5), avian metapneumovirus (aMPV), murine hepatitis virus type 3, porcine parvovirus and bovine respiratory syncytial virus. Materials and methods: The antiviral activity was determined by a titration technique that depends on the ability of plant extract dilutions (25 or 2.5 mu g/mL) to inhibit the viral induced cytopathic effect and the extracts' inhibition percentage (IP). Results: Two medicinal plant species showed potential antiviral activity. The Aniba rosaeodora Ducke (Lauraceae) extract had the best results, with 90% inhibition of viral growth at 2.5 mu g/mL when the extract was added during the replication period of the aMPV infection cycle. The Maytenus ilicifolia (Schrad.) Planch. (Celastraceae) extracts at a concentration of 2.5 mu g/mL exhibited antiviral activity during the attachment phase of BHV-5 (IP = 100%). Discussion and conclusion: The biomonitored fractionation of the active extracts from M. ilicifolia and A. rosaeodora could be a potential tool for identifying their active compounds and determining the exact mechanism of action.501012691275Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)