A series of particulate emission tests were conducted on cotton gins in New Mexico and California. All exhausts measured used high-efficiency cyclones as emission-control devices. Total suspended particulate (TSP) for all gins averaged between 0.03 and 0.04 grains per dry standard cubic foot (gr/dscf) of air emitted. The PM10 fraction of the TSP ranged between 35 and 69% depending on the method of determination. Levels of PM2.5 were determined to be between 0.4 and 2.5% of TSP. Opacity readings taken both during these tests and in earlier tests did not correlate with TSP and cannot be used to estimate TSP concentrations. The Hand-held Aerosol Monitor (HAM) correlates well with PM10 levels determined by the Coulter Counter and may be used by gin management for quick evaluation of emission-control systems.