Abstract. Let x(t), 0 < t < r, be a Gaussian process whose covariance function R(s, t) satisfies certain conditions. If G(x) satisfies some mild condition, then the quadratic integral L2-lim'2,kG(x(tk))&x(tk)2 along any sequence of paritions of [0, T] whose mesh goes to zero exists. The differential rule for x(t) is also derived.