The past 20 years have seen many advances in methods for the assay of drugs and other poisons in biological fluids, with consequent improvement in the reliability of results. Therapeutic drug monitoring, drugs of abuse and laxative/diuretic screening, and occupational health monitoring have developed considerably. The value of assays with overt medico-legal implications and which require a high degree of analytical expertise (such as brain death and child abuse screening, and cases of suspected iatrogenic poisoning) has become more clearly defined. Emergency toxicological analyses are now sometimes requested to monitor treatment with (e.g.) chelating agents. However, paracetamol apart, the growth in requests for other emergency toxicology analyses has been small, at least in the UK. What are the challenges for the future? With the increasing role of analytical toxicology, training and quality assurance should have a higher profile. Standardisation of the units used in reporting results should also be pursued. The need for simple, reliable, low-cost methods for the assay of drugs, pesticides and industrial chemicals in biological specimens remains, especially in developing countries. Interpretation of results remains difficult and can only be improved by construction of an improved data base. Biological monitoring to assess occupational/environmental exposure to metals, industrial chemicals and pesticides is likely to increase in importance. Interpretation of results in individual cases can here be simplified by regulation.