  The COMPTEL observations of the blazar-type quasar PKS 0528+134 in the energy
range 0.75 MeV to 30 MeV carried out between April 1991 and September 1994 have
been analyzed. During the first two years PKS 0528+134 was most significantly
detected at energies above 3 MeV. During the last year there is only evidence
for the quasar at energies below 3 MeV indicating a spectral change. The
time-averaged COMPTEL energy spectrum between 0.75 MeV and 30 MeV is well
represented by a power-law shape. Spectra collected from different
observational periods reveal different power-law shapes: a hard state during
flaring observations reported by EGRET, and a soft state otherwise. The
combined simultaneous EGRET and COMPTEL spectra indicate these two spectral
states as well. During low intensisty gamma-ray phases no spectral break is
obvious from the combined COMPTEL and EGRET measurements. For the gamma-ray
flaring phases however, the combined COMPTEL and EGRET data require a spectral
bending at MeV-energies. By fitting broken power-law functions the best-fit
values for the break in photon index range between 0.6 and 1.7, and for the
break energy between ~5 MeV and ~20 MeV. Because the flux values measured by
COMPTEL below 3 MeV in both states are roughly equal, the observations would be
consistent with an additional spectral component showing up during gamma-ray
flaring phases of PKS 0528+134. Such a component could be introduced by e.g. a
high-energy electron-positron population with a low-energy cutoff in their bulk
Lorentz factor distribution. The multiwavelength spectrum of PKS 0528+134 for
gamma-ray flaring phases shows that the major energy release across the entire
electro-magnetic spectrum is measured at MeV-energies.
