Microwave Fixation System preserves levels of enzyme-regulated neurotransmitters and metabolic substances in the brain at concentrations that exist in the living tissue, while brain size and structure remain unchanged. Uniform fixation of the entire brain is achieved without damage to the hypothalamus or other soft, deep-brain structures. Applicators and holders are available for animals from 20 to 500 g, and are interchangeable, making this system ideal for core facilities or individual laboratories. Two systems are available, differing in maximum power output of 5 or 10 kW.