Briefcase-sized analyzers, originally designed for monitoring emissions from land-based smokestack gases, have been adapted to shipboard use. The results are comparable to those of much larger, rack-mounted devices used on shore, or the multiple instruments used by Lloyd's Register on shipboard. Portable monitors are particularly useful for small vessels, and have been applied to hot exhausts directly out of turbochargers, instead of the usual smokestack measurements. The test protocol evolved during this study will be useful in monitoring diesel engine exhaust emissions, before and after application of emission reduction techniques to assess their efficacy.Initial shipboard testing was conducted on three 82-ft U.S. Coast Guard Cutters (WPBs). The test protocol used was one based on the ISO 8178 procedure (1), taking into account the speeds actually used by the vessels - their operating profile. Variables examined, aside from the effects of shaft rpm on the pollutant levels, were: water depth, current, effect of towing another boat, wind direction and sea state. Pollution was determined quantitatively as a function of power, and also fuel consumption. Shaft speed, as on larger vessels, showed the greatest effect on the pollutants - with much more scatter at lower speeds (<30% of full power). As expected, cold starts and accelerating transients had higher NOx levels than at steady state for short durations.