  We present the first FIR polarisation results of the OVV quasar 3C 279
obtained with ISOPHOT for two epochs in 1996 and 1997. We describe its integral
polarisation properties at a wavelength of 170 micron where the source shows a
maximum in its energy distribution. After a gamma-ray flare in January 1996, a
polarisation of 23 % closely aligned with the radio jet axis was measured in
July 1996. In June 1997, the polarisation degree had decreased to 6.5 % with a
less good alignment. On the other hand, the total 170 micron flux is the same
for both epochs. Our measurements provide additional constraints for the
multi-wavelength properties of synchrotron emission in radio jets and the
temporal evolution of these properties: they show that the FIR radiation of 3C
279 is optically thin and that its origin is very close to the core. The
variability of the FIR polarisation without any change of the total FIR flux
can be explained by a disordering of the magnetic field in between the core and
the first stationary VLBI radio knot.
