The Particle Measuring Systems (PMS) Forward Scattering Spectrometer Probe (FSSP-100) which was flown on the ER-2 during the Airborne Antarctic Ozone Experiment for the measurement of particles in polar stratospheric clouds has been evaluated and calibrated. The sample volume of the probe per 10-s sampling period increases from 257 cm3 for 1-μm particles to 412 for 15-μm particles, but there is substantial uncertainty in this value. Limitations in the measurements from this instrument and possible corrections are discussed. The uncertainty in the total particle mass measured by the probe may be as large as ¿100%. Recommendations are given for the processing of data from the FSSP used in this project. ¿ American Geophysical Union 1989