Abstract. An ordered and oriented 2-component link L in the 3-sphere is said to be achiral if it is ambient isotopic to its mirror image ignoring the orientation and ordering of the components. Kirk-Livingston showed that if L is achiral then the linking number of L is not congruent to 2 modulo 4. In this paper we study orientation-preserving or reversing symmetries of 2-component links, spatial complete graphs on 5 vertices and spatial complete bipartite graphs on 3 + 3 vertices in detail, and determine necessary conditions on linking numbers and Simon invariants for such links and spatial graphs to be symmetric.1. Introduction. Throughout this paper we work in the piecewise linear category. Let L = J 1 ∪ J 2 be an ordered and oriented 2-component link in the unit 3-sphere S 3 . Unless otherwise stated, the links in this paper will be ordered and oriented. A link L is said to be component preserving achiral (CPA) if there exists an orientation-reversing self-homeomorphism ϕ of S 3 such that ϕ(J 1 ) = J 1 and ϕ(J 2 ) = J 2 , and component switching achiral (CSA) if there exists an orientation-reversing self-homeomorphism ϕ of S 3 such that ϕ(J 1 ) = J 2 and ϕ(J 2 ) = J 1 [3]. If L is either CPA or CSA, then L is said to be achiral. Note that L may be both CPA and CSA (a trivial link, for example). The following was shown by Kirk-Livingston.