We theoretically analyze the optical response of an ultrathin film with accounting for the effects of creating two exciton states as well as their annihilation in an individual aggregate. We show that these two processes do not violate mirrorless optical bistability of the film found in the framework of the ground-to-one exciton state transitions but, contrary to that, act towards improving the conditions for bistability to occur. In particular, the killing action of inhomogeneous broadening of the one-exciton absorption spectrum may be considerably reduced due to the exciton-exciton annihilation process giving hope for creating a unit for an all-optical device based on such systems. (C) 2001 American Institute of Physics.