tokens: The present work has been planned in order to elucidate the effect of phenobarbital ( PB : 15 mg per rat of ingested dose ) on carcinogenesis when it is administered simultaneously with diethylnitrosamine ( DEN : 10 mg / kg / day ). Wistar rats ( 180 g ) were treated by DEN alone or by DEN + PB during 2 , 4 and 6 weeks according to our schedule for hepatocarcinogenesis .