Vertical profiles of virus-like particles (VLPs] and bacteria were determined by near-synoptic sampling through the water column and 15 to 25 cm into the sediment at 5 stations across the mouth of Chesapeake Bay, USA. VLPs were about 10 times more abundant in the pore water (grand mean = 3.6 X 10' VLPs ml-l) than in the water column (grand mean = 3.8 X 107 VLPs ml-l). Similarly, bacteria counts were about 3 tmes higher in the pore water (grand mean = 6.5 X 10' bacteria ml-l) than in the water column (grand mean = 2.4 X 106 bacteria ml-l). The virus to bacteria ratio (VBR) was greater in the pore water (range = 29 to 85) than in the water column (range = 12 to 17). The VBR was lowest in the water-over-boxcore samples and variable in the pore water. Counts of VLPs and bacteria were positively correlated in the water column, although neither was correlated to chlorophyll a. In the water column, VLP and bacteria counts exhibited significant differences among stations, with the highest values on the southern side of the Bay mouth. In the pore water, VLP abundance varied with depth and was negatively correlated to grain size. Bacteria abundance was highest at the sediment-water interface, decreased in the first cm of sediment, was uniform in the deeper horizons, and showed no significant relationship with grain size. Bacteria counts in pore water were not significantly different among stations. In contrast, VLP abundances in pore water were significantly different among stations, although they did not increase in abundance from north to south across the Bay mouth, as did counts of water-column VLPs. These are the first data ind~cating the abundance of VLPs below the surface layer of sediment In aquatic systems and demonstrate that VLPs are components of the sedimentary microbial community to at least 25 cm depth.