If a and b are elements of a Jordan algebra 31 we say that a and b operator-commute or o-commute if the multiplications Ra and 7?¡, commute. Here Ra is the linear transformation x->xa = ax of 21. The notion of o-commutativity has been introduced by Jordan, Wigner, and von Neumann [4] who called this concept simply commutativity. Since every Jordan algebra is commutative in the usual sense, the above change in terminology seems to be desirable. In this note we shall study the notion of o-commutativity for finite-dimensional Jordan algebras of characteristic 0. Our results are based on those of two previous papers [l; 2].1. If S3 is a subset of the Jordan algebra 21, then we denote by Sa(33) the subset of 21 of elements which o-commute with every ÔGS3. Evidently (Sa(33) is a subspace of 21, but, as we shall see presently, it is not always a subalgebra. Assume now that 21 is a special Jordan algebra, that is, 21 is a subspace of an associative algebra U closed relative to the Jordan multiplication {ab} = ab-+ba where ab now denotes the associative multiplication. We can now construct an example in which Sa (58) is not an algebra. Let a, b, c be finite matrices such that In this note we shall consider Sa(33) such that either 21 or 53 is semisimple. Our first result is as follows: Theorem 1. Let 2Í be a special semi-simple finite-dimensional Jordan