Transgenic animals are an experimental model of human diseases and enable us to study pathophysiological mechanisms, the interaction between genetic environmental factors and new therapeutic approaches incl. Their long-term effect. By using various methods it introduces into the genome of the experimental organism alien genes which become expressed. Mutated genes are introduced as well as the regulation sequence of expression of various genes, the sequence disrupting a certain gene or gene construction. Investigations of transgenic animals, whose production is rapidly increasing, are used in all spheres of medicine and biology. The author presents some examples from the sphere of oncology, cardiovascular, pulmonary, inflammatory and immunological diseases, human reproduction and early ontogenetic development, neuropsychiatric diseases and toxicology.