Carbohydrate contents in seawater, mucilage, and mucilage interstitial waters were analyzed during episodes of mucilage formation in the summers of 2000 and 2001 in the northern Adriatic Sea off Pesaro and in the Gulf of Trieste using 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) and 2,4,6-tripyridyl-s-triazine (TPTZ) assays. The significant presence of polysaccharides in seawater in the presence of mucilage has an important impact on the agglomeration processes forming gelatinous material (macrogels). Characterization of oligosaccharides in the water-soluble fraction of mucilage using HPLC/RI revealed maltose and pentaose as the main components.