Sampling, storage, and preparation of biological material for analysis are some of the most important factors in the study of trace elements in biomedical fields. If due care is not given to these factors, the resulting data may often be meaningless, regardless of the analytical technique chosen for analysis. A survey of the data in the literature would support this view, in which wide differences in the trace element composition of biological tissues have been observed, and not all these differences are attributed to variations in the biological systems.In this paper, the following points are discussed in detail: (A) Sampling and Storage Sampling methods and program. Contamination of the sample during sampling and storage. Changes in the composition during storage. Various storage methods for solid and liquid samples. (B) Sample Preparation Drying and ashing. Wet digestion. Different methods for preparing samples of hard, semihard, and soft tissues, and of biological fluids.