The current transport through GaAs/GaAlAs quantum well graded index (QW GRIN) injection lasers was studied by photocurrent spectroscopy. The quantum efficiency is assumed to be proportional to the absorption coefficient. The observed absorption edges are attributed to transitions between different QW subbands. Measurements have been carried out with transverse electric (TE) and transverse magnetic (TM) light polarization in order to study the anisotropy due tot eh quantum well and the influence of the GRIN waveguide. Different spectroscopic modes have been compared, among them a setup with rotating polarizer. After background subtraction the observed edges can be compared with existing theories. The factors affecting the lineform are outlined.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.