Abstract: Viruses play an important role in aquatic environments in bacteria and phytoplankton mortality and also in carbon and nutrient recycling through the lysis of living cells. However, the effects of nitrogen regenerated by viral lysis on the growth of picophytoplankton are rarely studied. This study investigated whether the presence of viruses has a positive effect on the daytime frequency of cell division in Synechococcus spp. in the coastal waters of the western subtropical Pacific Ocean. Using cell incubation with natural viral loads and reduced virus treatments, we characterized the abundance and frequency of cell division in Synechococcus spp. over time. Our results clearly showed that during the daytime as much as 30% of Synechococcus spp. were dividing in natural virus-containing samples, a proportion six times that found in the virus-diluted treatment groups (5%). These results suggest that viruses can exert significant effects on nutrient regeneration, enhancing daytime cell division rates in Synechococcus spp.