Introduction.There are several areas in recursive algebra and combinatorics in which bounded or recursively bounded 77?-classes have arisen. For our purposes we may define a Hj-class to be a set Path(T) of all infinite paths through a recursive tree T. Here a recursive tree T is just a recursive subset of co = {0,1,2,...}, which is closed under initial segments. If the tree T is finitely branching, then we say the /7?-class Path(T) is bounded. If T is highly recursive, i.e., if there exists a partial recursive function f:T-*co such that for each node n e T, f(n) equals the number of immediate successors of n, then we say that the 77?-class Path(T) is recursively bounded (r.b.). For example, Manaster and Rosenstein in [6] studied the effective version of the marriage problem and showed that the set of proper marriages for a recursive society S was always a bounded /7?-class and the set of proper marriages for a highly recursive society was always an r.b. /7°-class. Indeed, Manaster and Rosenstein showed that, in the case of the symmetric marriage problem, any r.b. 77?-class could be represented as the set of symmetric marriages of a highly recursive society S in the sense that given any r.b. n l -class C there is a society S c such that there is a natural, effective, degree-preserving 1:1 correspondence between the elements of C and the symmetric marriages of S c . Jockusch conjectured that the set of marriages of a recursive society can represent any bounded Z7?-class and the set of marriages of a highly recursive society can represent any r.b. /7?-class.These conjectures remain open. However, Metakides and Nerode [7] showed that any r.b. /7?-class could be represented by the set of total orderings of a recursive real field and vice versa that the set of total orderings of a recursive real field is always an r.b. /7°-class. Similarly, Bean [1] showed that the set of proper kcolorings of a highly recursive graph is always an r.b. 77?-class, while Remmel [13] showed that any r.b. 27j-class could be represented as the set of proper fc-colorings of a highly recursive graph G for any k > 3. In this paper we study an effective version of a combinatorial selection principle due to Rado. We shall prove that one can represent any bounded i7?-class as the set of "solutions" to the effective version of Rado's problem. What is actually interesting about this problem is that