Imidazobicycles having a quaternary nitrogen, i.e. imminium salts, are disclosed. Examples include derivatives of 6,7,8,9-tetrahydro-5H-imidazo[1,2-a]azepinium and 2,3-dihydroimidazo[2,1-b]thiazolium salts. The compounds are inhibitors of the Hedgehog pathway and therefore useful as antitumor agents and as probes of the function of Hedgehog-dependent systems.