SUMMARYMany hospital pharmacy laboratories undertake drug analysis in biological fluids for the production of pharmacokinetic data. The success of such an undertaking very much depends on the selection of a suitable analytical method and a proper approach to sample collection and handling. This paper surveys the main types of biological specimens taken from the patients for pharmacokinetic drug analysis and discusses factors that affect them during or subsequent to their removal. Guidelines are provided in specimen handling and dealing with many problems which could arise prior to actual analysis. By its very nature this paper brings in many disciplines, the full details of which are well beyond its scope, however, some discussion on pharmacokinetic and bioavailability methods in relation to sampling procedures is included to put the matter into a proper perspective. I N T R O D U C T I O NIn addition to the choice of a suitable analytical technique, analysis of drugs and metabolites in biological fluids for pharmacokinetic and bioavailability studies require detailed consideration of such factors as the methods for collection, handling, and preparation of samples before analysis, and stability of samples under various storage conditions. The preanalytical phase of drug analysis, though very important, does not always receive sufficient attention which is surprising because improper sampling and storage can alter the sample and consequently incorrect results can be obtained. Availability of sophisticated equipment has little meaning if the sample integrity prior to analysis is not maintained. This review attempts to remedy this situation and offers some general guidelines on ways of preparing samples for drug bioanalysis. Preanalytical treatment of those body fluids which are commonly used in clinical pharmacokinetic work, i.e. blood (plasma or serum), urine, saliva and cerebrospinal fluid (CSF), will be considered here. ANALYTICAL M E T H O D SPharmacokinetic studies in man involve quantifying of drug and/or metabolite levels in appropriate body fluids or tissues at any point in time following drug administration 285