www.pteridines.org
            Pteridines, Journal of ISP

www.i-med.ac.at  
            Innsbruck Medical University

www.bh4.org 
            BH4 - Tetrahydrobiopterin Homepage

www.schircks.com
            Schircks Laboratories, Home of Pteridines

www.ncbi.nlm.nih.gov  
            PubMed, National Library of Medicine

www.brahms.de
            BRAHMS Company, Hennigsdorf/Berlin, Germany, Neopterin Immunoassay Supplier

www.ibl-hamburg.com
            Immunobiological Laboratories, Hamburg, Germany, Neopterin Immunoassay Supplier

www.concile.de
            Concile GmbH, Freiburg, Germany, Neopterin Immunoassay Supplier

www.immundiagnostik.com
            Immundiagnostik, Bensheim, Germany, Tryptophan Metabolites Immunoassay Supplier