These techniques are surgical preparations that involve the implantation of catheters in order to gain access to the vascular system and the vascular beds of various organ systems. Catheters permit sampling or infusion to occur in a conscious animal with little or no stress. The large animal preparations are preformed for those investigators whose protocols address interorgan metabolism or protocols that require multiple samples over time. The catheterization techniques for small animals are used for blood collection or infusion in studies where interorgan metabolism or prolonged sampling is not required. Use of small animals is advantageous when, for example, the cost or availability of a reagent is limited. The surgical procedures for large animal preparations are preformed 14-17 days prior to an experiment and all catheters and flow measurement devices are buried subcutaneously at the time of surgery to maximize recovery and minimize post-operative care. The small animal surgical procedures are performed 4-7 days prior to experiments. Below are listed the types of surgical catheterization techniques that have been developed by the Core. We have identified the species for which the techniques are applicable.