Let A be a closed operator on a separable Hilbert space with the spectrum in the open right half-plane and a bounded Hermitian component, and let the resolvent of A be a Hilbert-Schmidt operator. The paper deals with the function h µ (A) = ∞ 0 (A + tI) −1 dµ(t),where µ is a nondecreasing function and I is the unit operator. We establish norm estimates and perturbations results for h µ (A). As particular cases the fractional powers and logarithm of A are considered.