  In this paper we introduce operator preinvex functions and es- tablish a
Hermite-Hadamard type inequality for such functions. We give an estimate of the
right hand side of a Hermite-Hadamard type inequality in which some operator
preinvex functions of selfadjoint operators in Hilbert spaces are involved.
Also some Hermite-Hadamard type inequalities for the product of two operator
preinvex functions are given.
