Two International Standards for measurement of asbestos in air by transmission electron microscopy (TEM) have been approved. A key feature of the ISO TEM methods is the ability, from a single examination, to derive fiber concentrations for comparison with all known legislated control limits, and to provide a coded description of the size and nature of each asbestos structure to assist in the interpretation of health effects. The direct-transfer TEM method for determination of asbestos in air (ISO 10312) was published as an International Standard in May 1995. Voting on an indirect-transfer TEM method (ISO 13794) has been completed, and the final draft has been submitted for publication. A method for determination of the concentration of inorganic fibers in air, based on scanning electron microscopy (SEM), has recently been submitted for voting as a Draft International Standard, currently designated as ISO/DIS 14966. A new working group, ISO/TC 146/SC 6/WG4, was formed in late 1996, to develop International Standards for sampling strategy for determination of asbestos and other mineral fibers in building atmospheres.