Some years ago we demonstrated the cytokinin-like activity of the synthetic N-phenyl-N′- benzothiazol-6-ylurea (PBU) and a relevant adventitious rooting adjuvant activity of symmetric urea derivatives devoid of any cytokinin-or auxin-like activity per se. Here we report the synthesis and the biological activity evaluation of nine symmetric or asymmetric ureas/thioureas, structurally related to PBU. None of them show cytokinin-like activity, ...