  We use the new results of the HEGRA detector on the TeV gamma-ray emission
from MKN 501 to set upper limits on the energy density of the cosmic infrared
background (CIRB). Contrary to previous interpretations of the gamma-ray
spectrum of MKN 421 as showing an intergalactic absorption cutoff at 5 TeV, the
observed spectrum of MKN 501 extends beyond 10 TeV and appears to be
unattenuated by gamma-gamma collisions with the low-energy
  CIRB photons. The upper limits on the CIRB intensity -- derived both assuming
an `a priori' shape for the CIRB spectrum and without model-dependent
assumptions -- are thus quite strong and come almost in conflict with the
observational evaluations based on deep surveys of extragalactic sources in the
near- and mid-IR. If spectra at TeV energies for extragalactic gamma-ray
sources like this for MKN 501 will be confirmed with improved statistics, we
may be forced to conclude that the process of gamma-gamma interaction in the
intergalactic space is more complex than expected and the average intergalactic
magnetic field extremely weak.
