Cerebrospinal fluid (CSF) can be collected either by lumbar puncture at the base of the spine using a hypodermic syringe or by withdrawal of cisternal fluid by puncturing the base of the neck. Although there are limited published reference data for quantitative drug concentrations in CSF, this clear fluid comprising mostly water is amenable to most routine methods of toxicological analysis. CSF may be of particular importance in alcohol-related cases where no vitreous humour is available, particularly if postmortem alcohol production is suspected. Like vitreous humour, CSF is anatomically isolated and less prone to contamination and bacterial invasion. Although it is more plentiful than vitreous humour, the lack of plentiful reference data limits its usefulness. However, CSF may be particularly useful in surgical death investigations.