In response to a request from the Directorate General for Health regarding the health impacts associated with environmental exposure to asbestos, the French Institute for Public Health Surveillance is collaborating with the Bureau of Geological and Mining Research and the Laboratory for the Study of Inhaled Particles to conduct a study on outcrops of asbestos-bearing rocks in mainland France. Corsica, which is the subject of a separate study, was not included in this study. The objective of the study is to assess current environmental exposures of the population to asbestos from these outcrops by describing the phenomena of fiber transfer into the air under various exposure scenarios. Only inhalation exposure, considered to be the primary route, is taken into account. The method employs two complementary approaches—qualitative and quantitative—for assessing exposure to asbestos fibers: expert judgment and metrology. Rock friability is a major factor in fiber emissions from an outcrop. It also appears that the mechanisms of rock disturbance are decisive in determining whether or not emissions occur. Depending on whether they are wind-driven or anthropogenic, mechanical disturbances can lead to vastly different emission levels. Under conditions of exclusively wind-driven erosion, measurement results show that asbestos fiber concentration levels near homes and in the vicinity of the outcrop remain very low (<1F>5um/L), even at sites with conditions most favorable for fiber release. In contrast, anthropogenic disturbances associated with human movement on the outcrop and manual handling of rock lead to high concentrations of fibers released into the air (several hundred F>5um/L). However, these emission levels must be put into perspective given the sporadic exposure circumstances and the small number of people visiting these sites located in high mountains, which are covered by snow for part of the year. Thus, among the 13 outcrops where the presence of asbestos has been confirmed in the exposed rock, two sites deemed to pose the highest risk of exposure have been subject to measures aimed at restricting access to the outcrops: La Girarde in the municipality of Termignon (73) and Val-de-Péas in the municipality of Château-Ville-Vieille (05). (R.A.)