We report herein the interaction of 2-phenyl-5-(4-diphenylyl) 1,3,4-oxadiazole (PBD) with alpha-, beta-, and gamma-cyclodextrins (CDs). It was found that the reaction patterns between PBD and CDs are remarkably different. alpha-CD can form a simple 1:2 (guest:host) inclusion complex with PBD, while beta-CD and gamma-CD can form nanotube with PBD at higher concentration of both PBD and CDs. It was also found that the interaction pattern of butyl-2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (butyl-PBD) with CDs is similar to that of PBD with CDs. On the basis of the above results, possible structures of these cyclodextrin nanotubes were discussed. (C) 2002 Elsevier Science B.V. All rights reserved.