A method for determination of weight concentrations of asbestos in the 0.01% to 10% range is described. The method is based on gravimetric matrix reduction, incorporating oxidation of organic materials, dissolution of acid-soluble components, and removal of large particle size materials by sedimentation or flotation, followed by analysis of the remaining material using a well-defined point counting procedure optimized for determination of mass concentration. The method has been validated by an inter-laboratory study with the Optical Microscope Laboratory of the Hong Kong Environmental Protection Department using laboratory-prepared standards with known weight concentrations of asbestos ranging from 0.1% to 6% in a wide variety of matrices. The results of analyses by both laboratories exhibit a linear relationship with the known weight concentration of asbestos, with a correlation coefficient of 0.97. The method provides a legally-defensible basis for determining whether the concentration of asbestos measured in a material is lower than or higher than a legislated standard of either 0.1% or 1% asbestos by weight.