To elucidate the effect of polyamines on adventitious root formation, we investigated the relationship between the frequency of adventitious root formation and the endogenous content of free polyamines in tobacco leaf segments which had been treated with polyamine biosynthesis inhibitors and polyamines. Adventitious root formation was inhibited in rooting medium (10$mu$M IAA) with methylglyoxal-bis(guanylhydrazone) (MGBG) or cyclohexylamine (CHA),and promoted with spermidine and putrescine. Treatment with high IAA (100$mu$M) medium plus CHA or MGBG promoted rooting up reversion of the rooting inhibition than the one treated with high IAA concentration alone. Spermidine promoted adventitious root numbers on low IAA (1$mu$M) medium when applied during culture period. The rooting inductive phase (in the presence of IAA) was determined by periodical transfer of leaf segments from IAA-containing medium of IAA free medium, and by changing polyamine contents, to be inductive phase. Putrescine and spermidine were accumulated to a maximum during the inductive phase. Therefore, the results point out the involvement of polyamines in inductive phase of acventitious root formation in tobacco leaf segments.