In this paper a hierarchy of predicate logic which refines the hierarchy by the number of quantor alterations is introduced and studied. Theorem 1 shows that the hierarchy constructed is the most refined in a certain sense. Theorem 2 describes hierarchy classes in terms of properties of the corresponding models. In Theorems 3 and 4, the connection between the hierarchy of formulas and the hierarchy of sets presented in [1] and the index sets is studied. © 1992 Plenum Publishing Corporation.