The seasonal distribution of marine viruses and their relationship with heterotrophic bacteria in the coastal and offshore area of the central and southern Adriatic was studied. Additionally, the percentage of high (HNA) and low (LNA) nucleic acid bacteria in the total number of bacteria and the distribution of heterotrophic nanoflagellates (HNF), as a major predator of bacteria, were studied as well. Viral abundance ranged from 3.55 to 27.32 × 10 6 virus-like particles mL -1 , and was on average 25-fold higher than bacterial abundances at all investigated stations. The highest viral abundances were found at coastal stations, especially in the area influenced by the rivers Krka and Jadro, whereas the lowest values were found in the open sea and in the coastal area of the southern Adriatic. No significant difference was established in the relationship of the viruses with HNA and LNA bacterial groups. The ratio between viruses and bacteria (VBR) was higher during the colder part of the year, which coincided with lower HNF abundance and vice versa during the warmer part of the year. This suggests that HNF grazing could be more important in controlling bacterial abundance during the warmer part of the year, and viral lysis during the colder part of the year.