Toxicological examination of biological samples of a certain case is a complex task which de- mands knowledge not only of modern analytical methods but also of the fate and effects of xenobiotics in organism. The evidence of unknown drugs and poisons in biological material is a difficult matter due to the broad variety of harmful substances and their unlimited possible mixtures, due to variable concentrations in a broad unpredictable range. In toxicology, there is the important question of the completness of evidence and correctness of chemical identification of individual substances. Generally, the validation of qualitative methods is less developed than the validation of quantitative methods. The evidence of unknown harmful substances in biologi- cal samples requires often the individual consideration about optimal attitude to a nonstandard toxicological case and prevent from application of uniform procedures in fixed combinations.

        Key words: toxicological analyses - toxicological evidence of unknown substances - detection and identification of poisons in biological material - validation of analytical methods