This chapter discusses blood collection and handling, preparation of serum and plasma for analysis, where blood for analysis may be obtained from veins, arteries or capillaries. Venous blood is usually used for most clinical chemistry estimations and is obtained by venipuncture. Arterial blood is mainly used for blood gas analyses. Area around the puncture site should be cleaned with an alcohol swab and allowed to dry. A tourniquet should be applied on the upper arm to obstruct venous blood flow and distend the vein. Sterile disposable needles and syringes should be used for collecting blood. The tourniquet should be released and then the needle withdrawn. If whole blood or plasma is desired for testing, an anticoagulant must be added to the specimen during collection. Separation of plasma from the cells should be done as soon as possible and is done by centrifugation. Serum is used for most other clinical chemistry analyses.