ABSTRACT. Let M n (F) be the algebra of nðn matrices over a field F of characteristic p Ù 2 and let Ł be an involution on M n (F). If s 1 Ò Ò s r are symmetric variables we determine the smallest r such that the polynomialis a Ł-polynomial identity of M n (F) under either the symplectic or the transpose involution. We also prove an analogous result for the polynomialwherer are skew variables under the transpose involution.