AbstractOut of a series of eleven related hetarylhydrazones four derivatives (ZIMET 124/73, ZIMET 38/74, ZIMET 44/69, and IMET 98/69), after subcutaneous administration (0.5 mmole/kg per injection), were found to possess significant antiviral activity against rapidly progressing and highly lethal Mengo virus encephalitis in mice. After peroral administration (2 mmole/kg per injection) only with IMET 98/69 significant protection was achieved. Drug treatments were given twice daily for 5 days. The effectiveness of compounds was evidenced by significant „rates of protection”︁. Possible relationships between the antiviral activity and the structure of compounds are disc