This volume presents aspects of cellular mechanisms and generalized functions related to import and export of substance, intracorporeal transfer and maintenance of the overall status of animals: the regulation of ammonia detoxification by metabolic mechanisms, the renal elimination of organic acids as metabolic end products, the unmodified elimination of ammonia across cell membranes and epithelia; the effect of morphological changes in the branchial epithelium in response to varying external conditions on acid-base and ionic regulation in fish; the regulatory role of natriuretic peptide hormones for osmoregulation and hemodynamics in fish; the modulation of Na+ and K+ channels, as well as Na+/K+ and proton pump activity by intracellular pH in high resistance epithelia; the character of intracellular signals controlling ionic and acid-base regulation in avian nasal gland cells; behavioral body temperature reduction as an alternative and energetically advantageous approach to increasing oxygen supply under conditions of hypoxia; the metabolic and external detoxification in animals exposed to high levels of hydrogen sulfide.