<jats:p><jats:bold>Isolation and Structure Elucidation of Pteridines (Lumazines) from <jats:italic>Russula sp. (Basidiomycetes)</jats:italic></jats:bold><jats:p>Extensive chromatogaphic separations and spectroscopic investigations have led to the isolation and identification of several water‐soluble pteridines from <jats:italic>Russula sp.</jats:italic>, the so‐called russupteridines, namely: 1‐(5‐amino‐2‐6‐dioxo‐1,2,3,6‐tetrahydeopyrimidin‐4‐yl)amino‐1‐deoxy‐<jats:sc>D</jats:sc>‐ribitol (<jats:bold>1</jats:bold>; a pro‐lumazine; first identification in a <jats:italic>basidiomycete</jats:italic>(; l‐deoxy‐l‐(6‐methyl‐2‐4,7‐trioxo‐1,2,3,4,7,8‐hexahydro‐pteridin‐8‐yl)‐<jats:sc>D</jats:sc>‐ribitol (<jats:bold>3</jats:bold>) and l‐deoxy‐1‐(2,4,7‐trioxo‐1,2,3,4,7,8‐hexahydeopteridin‐8‐yl)‐<jats:sc>D</jats:sc>‐ribitol (<jats:bold>4</jats:bold>); both compounds found for the first time in higher fungi; they belong to the components with the strongest violet‐blue fluorescence in <jats:italic>Russula sp.</jats:italic>; riboflavine (<jats:bold>6</jats:bold>; now recognized as an important yellow colorant in a great many of <jats:italic>Russula sp.</jats:italic>); russupteridine‐yellow I (= l‐(6‐amino‐7‐(<jats:italic>N</jats:italic>‐fromylimino)‐2,4‐dioxo‐1,2,3,4,7,8‐hexahydropteridin‐8‐yl)‐1‐deoxy‐<jats:sc>D</jats:sc>‐ribitol; <jats:bold>5</jats:bold>; a component with very strong fluorescence; the first derivative of the novel 6,7‐diamino‐lamazine); russupteridine‐yellow IV (= l‐deoxy‐1‐)(2,6,8‐trioxo‐2,4,5,6,7,8‐hexahydro‐1<jats:italic>H</jats:italic>‐imidazolo[4,5‐<jats:italic>g</jats:italic>]pteridin‐4‐yl)‐<jats:sc>D</jats:sc>‐ribitol (7)). Two further yellow russupteridines (yellow II and Yellow V) with very strong fluorescence have been isolated and characterized.