This study investigated the concentration-response relation between air pollution (nitrogen dioxide and particulate matter pollutants PM(10) and PM(2.5)) and cause-specific mortality. The population included all inhabitants of Oslo, Norway, aged 51-90 years on January 1, 1992 (n = 143,842) with follow-up of deaths from 1992 to 1998. An air dispersion model (AirQUIS; Norwegian Institute for Air Research (NILU), Oslo, Norway) was used to estimate levels of exposure in 1992-1995 in all 470 administrative neighborhoods. These data were linked to census, education, and death registries. A consistent effect on all causes of death was found for both sexes and age groups by all indicators of air pollution. The effects appeared to increase at nitrogen dioxide levels higher than 40 micro g/m(3) in the youngest age group and with a linear effect in the interval 20-60 micro g/m(3) for the oldest. An effect of all indicators on cardiovascular causes, lung cancer, and chronic obstructive pulmonary disease was also found in both age groups and sexes. The effects were particularly strong for chronic obstructive pulmonary disease, which appeared to have linear effects, whereas cardiovascular causes and lung cancer seemed to have threshold effects. Results show that vulnerable persons with chronic obstructive pulmonary disease and the elderly seem to be susceptible to air pollution at lower levels than the general population.