As one of the disciplines within forensic science, criminalistics deals with the analysis of evidentiary materials, relying heavily on chemistry. Two major challenges faced by the criminalist are individualization (evaluating the possibility that two items of evidence have a common origin) and reconstruction (analyzing evidence to determine the sequence of events in a crime scene). At present, only a few types of physical evidence can be truly individualized, such as fingerprints, jigsaw matches, footwear and tire prints, striations in tool marks, and ballistics evidence. However, new methods and improved instruments have allowed forensic scientists to come closer to their goal of associating items with a unique source. Scanning electron microscopy has proved especially useful in gunshot residue detection. Pyrolysis-gas chromatography has been a powerful analytical tool for the further characterization of synthetic fibers and paint samples. The combination of gas chromatography and mass spectrometry has become an indispensable tool in the war against narcotics by rapidly identifying drugs and determining their composition. Thin layer chromatography has improved forensic examination and comparison of synthetic fibers and has the advantage of being a nondestructive technique. Fusion microscopy also has been useful in identifying synthetic fibers. Plasma emission spectroscopy can categorize glass fragments into usage classes and helps individualize glass specimens. Serologists now can produce a far more detailed description of an individual's blood than just ABO groupings, and RIA procedures are available to assay various drugs, protein and steroid hormones, and other biologically important substances. In addition, RIA can be used when large numbers of samples must be assayed. Figures and 55 references are supplied.