The 1982-1983 El Niño event afforded the opportunity to develop criteria for the recognition of ancient El Niños using mollusks from archaeological sites along coastal South America. A combination of growth increment and stable isotope analyses indicated that elevated sea surface temperatures during large scale El Niños leave a record decodable from the growth patterns of selected bivalve shells. The intertidal venerid <i>Chione subrugosa</i> displayed a pronounced break in the valve margin profile following the 1982-1983 event but provided an inconsistent stable isotope pattern. The subtidal carditid <i>Trachycardium procerum</i>, on the other hand, preserved a discernible and diagnostic growth interruption as well as an expected trend in stable isotope indicators of salinity and temperature change. It is concluded that some of the major culturally disruptive El Niño events can be recognized in the geoarchaeological record by these techniques, specially if ancillary information, such as faunal distribution patterns, is also considered. Perhaps the most serious constraint upon application of this approach involves microstratigraphic resolution of shell midden deposits. Stratigraphic sampling of midden material should be accompanied, if possible, by sampling of proximal natural strata. The chances of discovery of major El Niño perturbations in the geoarchaeological record of shell middens is enhanced by the catastrophic nature of such events and by the indication that major El Niños have a high probability of being closely spaced in time.