The mortality of truck drivers and taxi drivers was studied in Reykjavík. The national mortality rate was used for comparison, and the follow-up lasted until 1 December 1988. The 868 truck drivers (28,788.0 person-years) had an excess of lung cancer deaths [24 observed, 11.2 expected, standardized mortality ratio (SMR) 2.14], but fewer deaths than expected from respiratory diseases (15 observed versus 30.1 expected). The SMR from lung cancer did not steadily increase as the duration of employment increased, nor did it change with the length of follow-up. The SMR values did not deviate substantially from unity for the taxi drivers. Since the high mortality from lung cancer among the truck drivers did not seem to be due to their smoking habits, it might have been caused by one or more occupational factors, especially in light of this group's exposure to engine exhaust gases.