Actinomycetes are well known as secondary metabolites producers and of high pharmacological and commercial interest. In this book, the following items are described and illustrated in details: Isolation, characterization and identification of different actinomycetes from rhizospheric soil of some cultivated plants. 2- Evaluation of the potentialities of some actinomycetes for production of IAA as phytohormone, L-glutaminase and antibiotics. 3- Detection of the most active antibiotics produced by actinomycetes as immunosuppressive agents. 4- Elucidation of the chemical structure of the most active immunosuppressive antibiotic compound produced by the active isolate.