  We present mid-infrared (4-18 micron) observations of the microquasar GRS
1915+105 obtained with ISOCAM, the camera on board the Infrared Space
Observatory (ISO), in 1996 April and 1997 October. The first observation
probably occurred during a flaring event with oscillating synchrotron emission.
The 1997 observation occurred a few days before a major relativistic ejection,
during a plateau state of inverted-spectrum radio emission and hard
quasi-stable X-ray emission. The K-M giant donor star in GRS 1915+105 cannot
account for the mid-IR emission and we discuss the possible additional
components depending on two absorption laws. Thermal emission from dust seems
unlikely. The flat mid-IR spectrum obtained during the plateau state is likely
to be synchrotron emission. It would be the first evidence of the infrared
extension of the radio synchrotron emission from the compact jets, although
optically thin free-free emission from an X-ray driven-wind from the accretion
disc cannot be excluded.
