The invention relates to medicine and concerns a method for the prophylaxis or treatment of diseases caused by (+)RNA-containing viruses which involves the use of an effective amount of glutaryl histamine or a pharmaceutically acceptable salt thereof. The invention also relates to a pharmaceutical composition for the prophylaxis or treatment of diseases caused by (+)RNA-containing viruses which contains an effective amount of glutaryl histamine or a pharmaceutically acceptable salt thereof. The present invention solves the problem of providing a novel agent which is effective in the treatment of diseases caused by (+)RNA-containing viruses of the enterovirus genus or of the flavivirus genus.