  We observed the energetic binary Cygnus X-3 in both quiescent and flaring
states between 4 and 16 microns using the ISO satellite. We find that the
quiescent source shows the thermal free-free spectrum typical of a hot, fast
stellar wind, such as from a massive helium star. The quiescent mass-loss rate
due to a spherically symmetric, non-accelerating wind is found to be in the
range 0.4-2.9 x 10E-4 solar masses per year, consistent with other infrared and
radio observations, but considerably larger than the 10E-5 solar masses per
year deduced from both the orbital change and the X-ray column density. There
is rapid, large amplitude flaring at 4.5 and 11.5 microns at the same time as
enhanced radio and X-ray activity, with the infrared spectrum apparently
becoming flatter in the flaring state. We believe non-thermal processes are
operating, perhaps along with enhanced thermal emission.
