From the aqueous extract of the red alga Digenea simplex, seven Dragendorff-positive compounds have been isolated and their structures determined by spectral and chemical methods. The taxonomic significance of their occurrence and possible biosynthetic relationships between some of these compounds are also discussed. Two are new metabolites that have been assigned the structures (R)-3-dimethylsulfonio-2-methoxypropanoare {1} and (S)-2-acetamido-5-trimethylammoniopentanoate {2}