WEAK LINE QUASARS AT HIGH REDSHIFT: EXTREMELY HIGH ACCRETION RATE SOURCES? THE SLOAN DIGITAL SKY SURVEY HAS DISCOVERED A REMARKABLE GROUP OF ~100 QUASARS WITH EXTREMELY WEAK EMISSION LINES IN THEIR REST-FRAME OPTICAL-UV SPECTRA. WE PROPOSE TO EXTEND OUR XMM-NEWTON OBSERVATIONS OF SUCH SOURCES AND OBTAIN IMAGING SPECTROSCOPY OF FIVE QUASARS OF THIS CLASS WITH A TOTAL EXPOSURE TIME OF 102 KS, PROVIDING -1000 PHOTONS PER SOURCE. THIS WILL ENABLE AN ACCURATE MEASUREMENT OF THE HARD-X-RAY PHOTON INDEX REQUIRED FOR A ROBUST DETERMINATION OF THE ACCRETION RATE IN EACH SOURCE. STEEP SPECTRAL SLOPES WILL INDICATE THAT HIGH ACCRETION RATES MAY BE RESPONSIBLE FOR THE INTRINSIC WEAKNESS OF THE OPTICAL-UV EMISSION LINES. THE PROPOSED OBSERVATIONS WILL YIELD CRUCIAL INSIGHTS ABOUT THE ACCRETION PROCESS AND BROAD EMISSION LINE FORMATION IN ALL ACTIVE GALACTIC NUCLEI.