The study of hydrothermal vents is conducted mostly through samples collected by submersible. Two vent fields on Axial Seamount, Juan de Fuca Ridge, have been visited at least three times each between 1983 and 1988 by Canadian, American, and Soviet workers. This study offers some comparative observations, but controlled experimentation was not conducted. After 5 years, unsampled vents appeared unchanged in gross aspects such as animal abundance, but those that had been sampled were depleted or gone. Changes at a sulphide deposit inhabited by tube worms were documented by a time-lapse camera over two years during which time both sulphide area and tube worm coverage decreased most dramatically immediately after sampling with submersibles. Vestimentiferans displaced from fluid flows were able to survive several weeks but were rarely seen emergent. Surfaces denuded of tube worms were repopulated by polychaete species previously known at this vent. Recruitment by tube worms to either the denuded mount or to settling plates was negligible. Some vent animals may be highly sensitive to disruption despite the naturally unstable nature of their habitat. Effects of sampling on long-term studies of vent animals, sulphide deposits, and vent effluents need serious consideration. ¿ American Geophysical Union 1990