Pteridines is an open acess international quarterly journal dealing with all aspects of pteridine research. Pteridines are heterocyclic fused ring compounds involved in a wide range of biological functions from the color on butterfly wings to cofactors in enzyme catalysis to essential vitamins. Of the pteridines, 5,6,7,8-tetrahydrobiopterin is the necessary cofactor of several aromatic amino acid monoxygenases, the nitric oxide synthases and glyceryl ether monoxygenase (GEMO). Neopterin plays an essential role in the immune system and is an important biomarker in laboratory medicine for diseases such as HIV, cardiovascular disease, malignant tumors, among others.