In this paper, we will consider a linear mapping between two JBW*-triples with the property that it preserves spectrum with respect to two arbitrary homotopes. We will show that such a map is a jordan homomorphism of those homotopes modulo the radical, which we characterize explicitly. 1. Introduction. The general problem of characterizing spectrum preserving linear maps between Banach algebras and Jordan-Banach algebras goes back to G. Frobenius and has seen much progress recently (see [4]-[8], [9], [10], and [25]). In [20], Frobenius showed that linear spectrum preserving maps φ from M n (C) onto M n (C) are of the forms φ(x) = axa −1 or φ(x) = ax t a −1 for some invertible matrix a. Hence, φ is a Jordan isomorphism. Aupetit, in [8], Theorem 1.3, has recently generalized this result to infinite dimensions, showing that all linear surjective spectrum preserving maps between W*-algebras and JBW*-algebras are Jordan isomorphisms. In the proof, the key point is that the spectrum function is lipschitzian around an idempotent in any semi-primitive Jordan-Banach algebra. It follows that spectrum preserving maps preserve idempotents. Consequently, the result is true whenever a linearly dense collection of idempotents are present.In this paper, we will generalize Aupetit's result to the larger class of JBW*-triples, which includes W*-algebras and JBW*-algebras. JB*-triples are a natural generalization of C*-algebras because, as shown by Friedman and Russo in [17], the range of a contractive projection on a C*-algebra is a JB*-triple. This fact also follows from the work of Kaup, who showed [26] that JB*-triples are are exactly those Banach spaces whose unit ball is a bounded symmetric domain. These objects have been much studied in the last twenty years from the point of view of both complex analysis [2], [26], [30] and C*-algebra theory [3], [11]-[13], [16]-[19].JB*-triples possess a ternary multiplication and thus the the spectrum must be defined with respect to a homotope as in [23]. We will prove that surjective linear maps which preserve such spectrum are Jordan isomorphisms of the homotope structure modulo the radical. More specifically, if φ is a linear surjective map between two JBW*-triples A and B which preserves spectrum with respect to the homotopes A a and B b , for elements a in A and b in B, then the cannonical map φ from A a onto B b / Rad(B b ) is a Jordan homomorphism. Furthermore, the kernel of φ coincides with Rad( A a ) and φ restricts to an isomorphism from A a / Rad( A a ) onto B b / Rad(B b ).