Measurements have been made in the manner in which device parameters vary during forward-biased operation of GaAs double-heterostructure lasers. The threshold current increases, but the slope external efficiency remains relatively constant. A conclusion is that optically absorbing or scattering centers are not the cause of degradation. The increase of threshold is attributed to an increasing nonradiative recombination component, the defect responsible for which is not yet determined. The important question regarding the role of optical flux is examined and it is shown that this is not the cause of the observed degradation in device characteristics.