Calmodulin serves as a regulator for various proteins, such as enzymes, kinases or phosphatases. It can also serve as Ca2+-dependent adaptor protein. Due to the previous evidence that retroviruses use host cell calmodulin for their proliferation, we focused on the description of functional and structural patterns of the interaction between Mason-Pfizer monkey virus matrix and human calmodulin. One of the methods used was hydrogen deuterium exchange.