Abstract: Let O be a polish space and B denote the family of Borel sets of O. Consider the set M of finite (positive) measures on the measurable space (O, B). Prohorov defined a distance II on M in such a way that II-convergence is equivalent to weak convergence and (M, II) is also a polish space. In this work we prove the II-continuity of the operations of addition (Mx MM) and scalar multiplication (R+ x M? M) and obtain, as a consequence of this results, some relations between the topological structures of M the set F of probability measures on (O, B) Ver menos