THE HOMOMORPHISM ON THE PTAK'S SUMP. Ptak [2] has defined a sum of a Boolean algebra and a quantum logic (i.e. an orthomodular lattice). In this paper we study a homomorphism on this structure. The main result is the relationship between homomorphism on the Ptak's sum that can be defined by finite homomorphisms on the quantum logic and the cardinality of the Boolean algebra.