Abstract: Twenty-eight new N-2-thiazolyl and thiazolinyl-N'-substituted phenylureaswere synthesized by the reaction of the heterocycles and substituted phenyl iso-cyanates.Their cytokinin activity was examined by cucumber cotyledon expansionbioassay.N-thiazolyl and N-thiazolinyl-N'-(m-chlorophenyl )-ureas showed a goodPGRactivity in comparison to Kinetin.The structure/activity relationship was dis-cussed.

Key words: N-2-thiazolyl substituted phenylurea, Thiazolinyl-N'-substitutedphenylurea, Cytokinin activity