Polymorphs of 8-chloro-6,11-dihydro-11- (4-piperidilidene) -5H-benzo.

Crystalline polymorphs of 8-chloro-6, 11-dihydro present-11 - {(4-piperidylidene} -5H-benzo {{[{5,6}]} {cyclohepta [1,2-b} {]} pyridine represented by formula (I), pharmaceutical compositions containing the polymorphs, and methods of using the polymorphs to treat allergic reactions in mammals such as man.