Aims: Our main interest is to check if programmed cell death (PCD) can occur in prokaryotic algae and if the morphological and biochemical features of PCD are conserved. Methods and Results: Using TUNEL labelling, fluorescence and light microscopy and DNA gel electrophoresis, we found that cell death with features similar to those in metazoan PCD could be induced in different Anabaena strains after exposure to univalent-cation salts at moderate concentration. These features included specific DNA fragmentation, cytoplasmic vacuolation, and the progressive disorganization, fragmentation and subsequent autolysis of the cell corpse. Further analyses of cell viability and proteinase activity revealed that increased protease activities, decreased DNA content, and loss of plasmalemma integrity were related to the PCD process. Conclusions: The results showed that like PCD in eukaryotes, PCD in Anabaena is an active process, and is an adaptation to adverse environments. The features of PCD shared between eukaryotes and Anabaena suggest that PCD mechanisms are conserved during evolution. Significance and Impact of the Study: The results will contribute greatly to our understanding of PCD origin and evolution, and are potentially useful in controlling the deluge of algae in some lakes.