Recently, the issue of potential health hazards by Diesel exhaust emissions - in particular, lung cancer risk by inhalation of Diesel soot - has been addressed improperly in SAE publications. Some unqualified statements portrayed Diesel soot as an actual human health risk of measurable proportions for the general public, and the present situation was referred to as alarming. Such contentions will be rebutted in this paper, and an attempt is made to put the health aspects of Diesel exhaust emissions and any associated lung cancer risk into proper perspective.Evidence is presented for common urban levels of general particulate air pollution containing all the Diesel soot to which the public is exposed to have no significant relation to the prevalence of lung cancer in urban areas. Furthermore, epidemiological studies of occupational exposure to Diesel exhaust emissions are demonstrated to be either negative or inconclusive. At best, such studies gave some very weak and disputed results indicating that, if existing, lung cancer risk from ambient airborne concentrations of Diesel soot must be extremely low. The same conclusion can be drawn from an indirect approach of deriving lung cancer risk by a comparative potency method.The implication that a potential health hazard may result from Diesel soot inhalation came entirely from in vitro and in vivo laboratory exposures. The most recent in vivo laboratory efforts are briefly described, and it is shown that final answers are not yet available. However, there is a body of experimental evidence about mutagenic and carcinogenic properties of some components of Diesel soot exhausts, and, although this applies also to extracts of particulate urban pollution and to condensates of gasoline engine exhaust, this might be the limited foundation on which “regulatory scientists” could base their decision to label Diesel soot a potential carcinogen no matter how low the actual human risk may be.Although publicly perceived as a health protection measure, the U.S. Emission Standards for particulate Diesel exhaust are not based on potential health hazards but have been promulgated exclusively on the basis of environmental aspects. It would be inconsistent then to mandate them for reasons of human health risks.