The nucleotides and nucleoside diphosphate monosaccharides (NDP-sugars), UDP-galactose, UDP-glucose, UDP, ATP, ADP, ADP-glucose, AMP and NAD, some of which are involved in carrageenan biosynthesis, were identified in the two carrageenophytes Calliblepharis jubata and Solieria chordalis and quantified by high-performance liquid chromatography (HPLC). Of several extraction procedures evaluated, a freeze-thaw step followed by formic acid (1 M) extraction was the preferred method. The pool size of nucleotides and NDP-sugars differed between the two algal species, which may be related to their growth state. Calliblepharis, which was not growing actively, had larger pools than Solieria, which was in an active growth phase. Using an HPLC method UDP-D-glucose-4-epimerase activity was measured in cell-free extracts of both algae, for the first time in a carrageenophyte.