This thesis examines the use of nail as an alternative biological specimen in forensic toxicology. Nail is a difficult analytical matrix from which to extract drugs because of its tough physical composition, based on keratin. The initial part of the project investigated the use of a cryogenic grinding method for fingernail clippings. Grinding at liquid nitrogen temperatures was found to be an effective procedure and the conditions were optimised to a two or three cycle programme of freezing and grinding. Small particle sizes were obtained of approximate size 1µm. It was established that drugs could be extracted directly from nail powder with a range of solvents without the need for alkaline hydrolysis. Methanol was found to be the most effective extraction solvent, which also gave the lowest number of co-extracted interfering compounds. This procedure was subsequently used with nail samples from different types of forensic cases, including cannabis, heroin and steroid abusers. Cryogenic grinding of nail was evaluated as an extraction method for cannabinoids in nail clippings from chronic cannabis smokers. This method was also compared to the alkaline hydrolysis method. Fingernail clippings were collected with prior informed consent from volunteers attending the Edinburgh Drug Addiction Study (EDAS) clinic. The collected nail clippings were decontaminated and divided into two groups: the first group was extracted with methanol after pulverisation in a liquid nitrogen cryogenic mill; the second was extracted with ethyl acetate after hydrolysis in sodium hydroxide. In both groups deuterated cannabinoids were used as internal standards. Both sets of extracts were derivatised with BSTFA before being analysed by gas chromatography – mass spectrometry (GC-MS). Cannabidiol, ?9-tetrahydrocannabinol and 11-hydroxy-?9-tetrahydrocannibinol were quantified in both sets of extracts. 11-nor-?9 –tetrahydrocannabinol-9-carboxylic acid was only identified and quantified in the extracts resulting from the cryogenic grinding method. Cannabinoid concentrations were very low, in the range 0-4 ng/mg. These results strongly support the use of nail as a biological specimen for the detection and quantification of past exposure to cannabis, and secondly, they indicate that grinding with a cryogenic mill is a useful procedure, which yields simultaneous results for the primary psychoactive cannabinoid and its metabolites. Cryogenic grinding was then evaluated for the extraction of opioids in nail in comparison with the conventional alkaline hydrolysis method. Finger and toe nails were collected from donors with informed consent.