Information on organism density and biomass is fundamental to understanding of community ecology and biological productivity at deep-sea hydrothermal vents. The traditional approach in benthic ecology has been to obtain this information through quantitative sampling. The generally small area and restricted distribution of vent communities and their location in deep water require that ecological studies use manned or unmanned submersibles for primary data gathering. Since most vent communities occur on hard substra, sampling requires the use of tools mated to submersible manipulators to remove organisms from basalt or sulphide surfaces. Surfaces are inevitably irregular and quantitative collection is difficult. As well, sampling is destructive and can have a significant impact on processes that are under investigation such as faunal community and habitat changes (Tunnicliffe, 1990; Sarrazin et al., 1997). This paper presents examples of how submersible-gathered video imagery can be used in combination with other methods to determine organism density at hydrothermal sites in contrasting geological settings. Use of video imagery minimizes habitat perturbation and, because it is non-destructive, permits time-series studies of individual vents and groups of organisms.