Positive Modal Logic (PML) is the logic of Kripke structures in a language containing conjunction, disjunction and modal operators, but no negation or implication. The class of algebras canonically associated with PML forms a category which is dually equivalent to certain topological spaces (Priestley spaces) endowed with relations, which are called K+-spaces. The talk is about the presentation of the following result: The category of K+-spaces is equivalent to the category of coalgebras of a certain endofunctor on Priestley spaces.