Capillary electrophoresis, the modern approach to instrumental electrophoresis, is probably the most rapidly expanding analytical technique that has appeared in recent years. In the hands of forensic toxicologists, capillary electrophoresis (CE) represents a powerful new analytical tool, which has proved suitable for the investigation of illicit drugs in seized preparations and also in complex biological matrices, among which is hair. CE can be applied according to different separation mechanisms, and among those that are toxicologically relevant are capillary zone electrophoresis and micellar electrokinetic capillary chromatography, which display different selectivities. For the investigation of hair for drugs of abuse, capillary electrophoresis proved effective, providing simultaneous determinations of different drugs without derivatization, with acceptable sensitivity (typically better than 1 ng of drug per mg of hair). The possibility of carrying out determinations of the same analytes, based on different separation mechanisms (capillary zone electrophoresis and micellar electrokinetic chromatography) with the same instrumentation, simply changing the buffer composition, provides an interesting possibility of 'internal' confirmation of the results.