This supplement to the NIOSH Manual of Analytical methods contains 15 methods, three new chapters and updated Contents, Method Finder and indexes as well as errata replacement pages. The section on the development and evaluation of methods discusses preliminary experimentation, recovery of analyte from medium, stability of the analyte on the medium, feasibility of analyte generation, capacity of the sampler and sampling rate, sampling and analysis evaluation, sample stability, precision bias and accuracy of analysis, field evaluation, and documentation. The application of biological monitoring methods is considered with emphasis on air monitoring, biological monitoring of exposure, biological monitoring of effect, biological matrices, selection of methods, sampling strategy, quality assurance, ethical considerations, laboratory safety, reference levels in the interpretation of results and variability. The section on aerosol photometers for respirable dust measurements discusses the principles of operation, sampling considerations such as safety and applications, data acquisition and treatment including calibration and operation, and instruments. Portable electrochemical sensor methods are discussed along with portable gas chromatography.