A unicellular cyanobacterium (Synechococcus) and its cyanophage were both isolated from a reservoir in Korea. Although morphologically similar to AS-1, the cyanophage differs from cyanophage AS-1 in some respects. The burst size in the light is approximately 100 plaque-forming units (PFU)/cell. Replication of the virus also occurs in the dark, releasing about 10% of the virus particles observed in the light. Na+ is not necessary for adsorption.