In this paper the reoccurring question of whether the life insurance industry's largest insurers possess and benefit from unique mortgage investment opportunities is examined. A portfolio adjustment model is presented which incorporates mortgage commitment behavior. Using this model and data for 15 insurers, speed of adjustment parameters are estimated for each insurer. The speed of adjustment, which is utilized as a measure of mortgage lending efficiency, is found to be invariant with respect to insurer size. This evidence suggests that the likelihood of significant aggregation bias in previous econometric work on life insurer mortgage investment is quite low.