1. Introduction. In the theory of ring extensions, the notion of a bitranslation (our terminology, for the definition see below) plays the role of automorphisms in group extensions. Bitranslations were studied by HOCHSCmLD [5] for algebras (,,multiplications", they aye also linear transformations); by CLIFFORD [2] for semigroups (,,pairs of linked left and right translations", where only the multiplicative part of the definition is retained); by RfiDEI [9] (,,Doppelhomothetismen") and MAC LANE [7] for rings (,,bimultiplications"), among others.Under a natural addition and multiplication, the set of bitranslations of a ring itself forms a ring. RfiDEI [9] defines a holomorph of a ring R as a (natural) split extension of R by a maximal ring of permutable bitranslations. It turns out that R may have more than one holomorph but that otherwise these have several properties analogous to the properties of the holomorph of a group. A number of properties of a ring holomorph have been established by RfiDE~ [8], [9], SZENDREI [10], VAN LEEUWEN [6], and WEINERT and EILHAUER [11].The purpose of this paper is to study the ring Y2(R) of bitranslations of a ring R for which czfl=fl~=0 for all flCR implies a=0 (see [5], [7], [11]). In this case Y2(R) is a ring of permutable bitranslations and the split extension of R by O(R) is the unique holomorph of R. The analogy with the group holomorph is in this case much stronger than in the case of an arbitrary ring. Section 2 contains most of the necessary definitions and notation. We are mainly concerned with rings R satisfying the above condition; for such R, in Section 3, we establish several properties of Q(R), and in Section 4, characterize s~(R) in several ways. We conclude in Section 5 by constructing Q(R) for a ring R which is of a special kind but need not satisfy the above condition, and derive several consequences of this result.It is of interest that the theory of ideal extensions of semigroups is quite similar to the theory of ring extensions, at least as far as multiplication is concerned (see [2] and 4.4, [3]). Even though the multiplicative part of a ring is a semigroup, this still seems surprising in view of very different definitions of extensions in semigroups and rings.From the results of Sections 3 and 4, we see that for a ring R satisfying the above condition, g2(R) plays the role of a ,,holomorph" of R (cf. ~ 54, [8]).