The role of small ice crystals in cirrus and the use of the FSSP (Forward Scattering Spectrometer Probe) to characterize the small crystal mode continues to be uncertain, although new evidence in recent studies indicate that FSSP may, given some criteria, measure adequately the small ice crystal mode for D < 50 µm. Since more researchers are doing this now, there should be studies comparing the size distributions (SDs) derived from the existing FSSP data. Earlier microphysical parameterizations have ignored FSSP data. This study will focus on one particular tropical cirrus cloud parameterization (McFarquhar and Heymsfield 1997). Microphysical and radiometric data from the Central Equatorial Pacific EXperiment (CEPEX) were used to evaluate ice crystal SDs, including measurements from the FSSP. McFarquhar and Heymsfield used VIPS (Video Ice Particle Sampler) data to determine the small crystal mode. We are presenting the difference between the VIPS and FSSP in terms of small ice crystal concentrations and the properties that depend on the SD shape. The results and differences between the VIPS and FSSP data will be presented at the conference.