AbstractThe in vitro antiviral activity of a freeze‐dried methanolic extract of the bulbs of Zimbabwean Crinum macowanii was determined in Vero cells infected with a number of exotic RNA viruses. At a concentration of 32 μg/mL, the crude methanolic extract reduced by 100% the viral cytopathic effect in Vero cells infected with yellow fever virus, and caused a 70% inhibition of the viral cytopathic effect in cells infected with Japanese encephalitis virus. No evidence of cytotoxicity was observed at this concentration. The freeze‐dried extract inhibited the replication of the above mentioned viruses by 100% at a concentration of 10 μg/mL. No cytotoxicity was seen at this concentration.