In December 1987, 10 portable nicotine and respirable particle measuring instruments were employed on 4 Boeing 747 flights, placed in all passenger classes and zones, in randomly selected non-perimeter seats, to assess environmental tobacco smoke (ETS). Measurements integrated the nicotine particle concentrations over the duration of the 5-h Tokyo-Hong Kong-Tokyo flights and over each half of the 14-h New York City-Tokyo flights. Number of cigarettes smoked per minute in sample areas explained a significant proportion of variability in the observed nicotine and respirable particle levels. The all-daytime Tokyo-Hong Kong-Tokyo flights with a different seating configuration showed higher levels of ETS variables. The cause cannot be identified from the six flight segments studied. Levels of ETS observed in these 747-100 and -200 flights (with all air conditioning packs operating) were lower than those observed in narrow body 727/737 aircraft, on short flights, in prior related tests. The 747's five air conditioning zones are reasonably effective in keeping ETS within the respective zones, and discharging it with relatively little entry into non-smoking areas.