Let X and Y be spaces and M be an abelian group. A homotopy invariant f : [X; Y] → M is called straight if there exists a homomorphism F : L(X; Y ) → M such that f([a]) = F([a]) for all a ∈ C(X; Y ). Here {a} : {X} → {Y} is the homomorphism induced by a between the abelian groups freely generated by X and Y and L(X; Y) is a certain group of "admissible" homomorphisms. We show that all straight invariants can be expressed through a "universal" straight invariant of homological nature.