Accurate measurement of atmospheric aerosol from aircraft platforms is of importance to a variety of research interests. Representative measurement of aerosol from aircraft-aspirated systems requires special efforts in order to (1) maintain near isokinetic sampling conditions, (2) estimate aerosol losses in the sample system, and (3) obtain a measurement of sufficient duration to be statistically significant for all sizes of interest. This last point is especially critical for aircraft measurements which typically require fast response times while sampling in clean remote regions. Here we present size-resolved tests, intercomparisons, and analysis of aerosol inlet performance as determined by a custom laser optical particle counter. Measurements discussed here took place during the Global Backscatter Experiment (1988-1989) and the Central Pacific Atmospheric Chemistry Experiment (1988). System configurations are discussed including (1) nozzle design and performance, (2) system transmission efficiency, (3) nonadiabatic effects in the sample line and its effect on sample line relative humidity, and (4) the use and calibration of a virtual impactor. ¿ American Geophysical Union 1992