A comparison of methods to measure cooling tower drift was performed at MIT, with participants from Belgium, the U.S. and the Federal Republic of Germany. The test environments differed according to droplet mass flux, droplet size distribution and gas speed. Cases tested included both mechanical and natural draft cooling tower environments. Among the instruments tested are the pulsed laser light scattering system (PILLS), sensitive paper and other sensitive surface droplet impaction systems, isokinetic drift mass flux measurement systems and photographic systems. The instruments tested varied widely in their capabilities, with droplet sizing instruments being more effective in low load, small droplet size spectrum situations, and isokinetic mass and chemical assay techniques being most accurate in high load, large droplet distribution cases.