The centralizer of a square-central skew-symmetric unit in a central simple algebra with orthogonal involution carries a unitary involution. The discriminant algebra of this unitary involution is shown to be an orthogonal summand in one of the components of the Clifford algebra of the orthogonal involution. As an application, structure theorems for orthogonal involutions on central simple algebras of degree 8 are obtained.Throughout this paper, F denotes a field of characteristic different from 2. Let A be a central simple F -algebra of degree n = 4m, for some integer m, endowed with an involution σ of orthogonal type. In the first two sections, we assume that the algebra A contains an element θ such that σ(θ) = −θ and θ 2 = a ∈ F . We denote byà the centralizer of θ in A. Since θ is skew-symmetric, σ induces an involutionσ onÃ, and (Ã,σ) is a central simple algebra with unitary involution of degree 2m over theétale quadratic extension F (θ) of F .With this data, we may associate two different central simple algebras with involution, namely the Clifford algebra of (A, σ), and the discriminant algebra of (Ã,σ), both endowed with their canonical involution (see [14, §8, §10]). Our aim in this paper is to relate these two algebras with involution.Reversing the viewpoint, one can show that every central simple algebra over a quadratic extension of F of even degree 2m endowed with a unitary involution and of exponent 2, can be embedded in a central simple F -algebra