Variability in the structure of the meiobenthic copepod communities was studied among three vent sites on the East Pacific Rise. One of the sites was dominated by the mussel Bathymodiolus thermophilus, and the other two of the sites were dominated by the tubeworm Riftia pachyptila. In addition to the differences in the dominant megafauna, the maximum temperatures were much lower at the mussel-dominated sites, and the temperature to sulfide ratio was different between the tubeworm-dominated sites. A total of 22 vent endemic siphonostomatoid copepod species and 5 harpacticoid copepod species were identified among the three sites. Copepod abundance was low at all sites ( 1 - 31 ind. 10 cm(-2)). Species richness ranged from 6 - 14, Shannon-Wiener diversity indices from 1.3 - 2.3, and Pielou's evenness indices between 0.6 - 0.9 were found. Differences were detected in abundance and Shannon-Wiener diversity between the mussel site and one tubeworm site. Multivariate analyses pointed to a relative homogenous mussel bed community and a heterogenous tubeworm community. The majority of species were primary consumers feeding on detritus. Both copepod sexes and, for the first time, all copepodite stages were detected in the samples.