  A light pseudoscalar coupled to two photons would be copiously emitted by the
core of a supernova. Part of this flux would be converted to $\gamma-$rays by
the galactic magnetic field. Measurements on the SN1987A $\gamma-$ray flux by
the Gamma-Ray Spectrometer on the Solar Maximum Mission satellite already imply
a bound on the coupling $g < 3 \times 10^{-12}$ GeV$^{-1}$. The improved
generation of satellite-borne detectors, like EGRET or the project GLAST, could
be able to detect a pseudoscalar-to-photon signal from a nearby supernova, for
allowed values of $g$.
