This is the fourth volume of Standard Operating Procedures (SOPs) compiled from documents prepared in these laboratories in part fulfilment of the requirements of various Good Laboratory Practice (GLP) regulations and guidelines. SOPs have now become an everyday feature of work in most industrial and contract toxicology laboratories. They provide a written definition of the mechanics of unit operations which together comprise the framework for experiments in safety evaluation. Metabolic studies and analytical chemistry are closely linked to toxicology since they embody essential aspects of the overall assessment of product safety. Some authorities consider certain parts of these subjects to be outwith the scope of the GLP requirements but for the reasons stated this is contrary to our own view. We have tried where possible to define in SOP format for use in our own laboratories the unit operations involved in these disciplines and they form the basis of this volume. Some relevant material from previous volumes has been brought together in updated form and is also presented here for completeness. Dr I P Sword Managing Director Inveresk Research International Musselburgh EH21 7UB Scotland ix Introduction GENERAL 1. The Food and Drug Administration of the US Government published its Good Laboratory Practice Regulations for Non-Clinical Laboratory Studies in the Federal Register (22 December 1978). The Regulations are the culmin­ ation of a number of years of investigation into the standards to which safety evaluation studies were performed in laboratories in the USA.