The aquatic cyanobacterium Nostoc verrucosum forms macroscopic colonies, which consist of both cellular filaments and massive extracellular matrix material. In this study, the physiological features of N. verrucosum were investigated and compared with those of the anhydrobiotic cyanobacterium Nostoc commune. Nostoc verrucosum cells were sensitive to desiccation, but tolerant of freeze-thawing treatment in terms of both cell viability and photosynthetic O(2) evolution. Natural colonies of these cyanobacteria contained similar levels of chlorophyll a, carotenoids, the UV-absorbing pigments scytonemin and mycosporine-like amino acids, and uronic acid [a component of extracellular polysaccharides (EPS)]. EPS from both N. verrucosum and N. commune indicated low acidity and a high affinity for divalent cations, although their sugar compositions differed. The WspA protein, known to be a major component of the extracellular matrix of N. commune, was detected in N. verrucosum. Desiccation caused similarly high levels of trehalose accumulation in both cyanobacteria. Although previously considered relevant to anhydrobiosis in the terrestrial cyanobacterium N. commune, the data presented here suggest that extracellular matrix production and trehalose accumulation are not enough for standing extreme desiccation in N. verrucosum.