For years statistical analysis has been applied to different areas of the natural and applied sciences to determine the degree of confidence that can be placed in research results. This work is a good example of how statistics can be applied to toxicology to enable conclusions and inferences to be made about important areas of interest such as the drugs and driving situation in New Zealand. Two thousand uninjured drivers (Study 1) who had provided an evidential blood alcohol sample, were also tested for cannabis, methamphetamine, benzodiazepines and morphine to determine the incidence of drug use by drinking drivers. To determine the proportion of drivers killed in car crashes who had used drugs and/or alcohol, two hundred and twenty nine fatally injured drivers (Study 2) were tested for alcohol, cannabis, methamphetamine, morphine, benzodiazepines and neutral and basic medicinal drugs that might have an effect on driving performance. Alcohol, cannabis and their combination were found to be the most prevalent drugs used by drivers. The analytical methodologies used were developed and validated by the Institute of Environmental Science and Research Ltd., where this work was carried out. These techniques involved liquid-liquid and liquid-solid extractions, immunoassays and chromatographic techniques for screening and confirmation assays. The statistical analysis of the results was done under the supervision of the Institute's biostatistician. An approach to cannabis culpability, intended to elucidate the role of this drug in car crashes, was applied to the Study 2 results. The number of samples collected during one year of research was not sufficient to enable statistically robust conclusions to be drawn. Cannabis use is illegal in New Zealand but drugs (different to alcohol) are not regularly tested at the roadside. This work as part of a cross-departmental project titled Drinking and drugged driver control: delineating the problem is expected to support the establishment of strategies designed to reduce the road toll and possibly include the screening of non-alcohol drugs in serious and fatally injured drivers.