The subantarctic frontal zone surveyed during the April-May 1991 SUZIL cruise in the Crozet-Kerguelen-Amsterdam area shows a strong horizontal (north to south) gradient of dissolved silicate, increasing with depth, from 5 to 10 µmolSi kg-1 at 100 m, and 10 to 70 µmolSi kg-1 at 600 m. The northern limit of this frontal zone, which is formed by the confluence of the Subtropical and Subantarctic Fronts, is delimited at the surface by the 2 µmolSi kg-1 silicate isoline. Silicate-salinity diagrams also allow different water regimes to be positioned relative to the frontal zone. This sloping interface is between two water bodies, one to the north with more saline subtropical waters of less concentrated silicate than the southern one, corresponding to subantarctic waters which are less saline and richer in silicate. It is concluded that dissolved silicate can be used as a useful tracer of frontal zone water masses in the Indian sector of the Southern Ocean, providing a sound complement to other hydrographic data.