The deep-sea tubeworm Riftia pachyptila and its endosymbiotic bacteria are thought to be major primary producers of the East Pacific Rise hydrothermal vent ecosystem. Tube production rates were measured for worms maintained alive in pressure aquaria. These rates (y) correlate to the fresh weight (x) of individuals, following an almost square-root relationship (y = 0.192x(0.492)). Extrapolation of experimental data to in situ animal densities (in dense clumps) leads to rates that may exceed 1 g C m(-2) d(-1) for worms from the Parigo site (13 degrees N). Thus, vestimentiferan tube growth alone would indicate that this vent site is a remarkable benthic hotspot for carbon production. Finally, it seems that these rates differ depending on the in situ origin of the animals, thus suggesting that in the future this type of experiment may provide quantitative information concerning the vitality of different vent sites.