Patients with hyperargininemia have an arginase deficiency which leads to blockade of the urea cycle in the last step with several clinical symptoms. Owing to the arginase deficiency this patients accumulate arginine which leads to eventual alternative yet unknown pathways of arginine metabolism. These clinical and biochemical findings intensified the research on guanidino compounds. It has been shown that most of the guanidino compounds are epileptogenic. Therefore we investigated the levels of 12 guanidino compounds in serum and brain of audiogenic sensitive rats. The changes of some guanidino compounds in serum and brain will be discussed.