The changes of the distribution patterns of some dinoflagellates considered as biological indicators showed the development of the 1982--1983 El Ni¿o. During El Ni¿o conditions the density of dinoflagellates was diminished, but there was a larger number of species, many of which are rarely found in this region. Protoperidinium obtusum, as indicator of cold coastal waters, disappeared almost completely during El Ni¿o 1982--1983, but it was very abundant when the conditions returned to normal. Ceratium breve, an idicator of equatorial surface waters, during normal conditions is restricted to the northern area up to 5 ¿S; during El Ni¿o it was distributed up to 15 ¿S. Several species indicators of warm waters were widely distributed during El Ni¿o 1982--1983 but are very rare or absent during normal conditions. ¿ American Geophysical Union 1987