ESR dating of marine mollusc shells is an important tool in coastal geomorphology as well as in palaeosea-level and other research. Some severe problems, however, remain as far as the accuracy of the dating results are concerned. Case studies of Patagonian Middle and Younger Quaternary marine terraces help to illustrate the potential of an improved ESR dating technique. It can be demonstrated that a discrimination of Holocene, Last Interglacial, Penultimate Interglacial and “older” samples is possible. A chronostratigraphic separation of the well-known Last Interglacial substages 5a, 5c, and 5e is still missing, partly due to the misleading accuracy of ESR dating results. Consequently, it cannot be decided yet whether the morphologically well-conserved Last and Penultimate Interglacial age substages result from a relative sea-level fall (glacioeustatic and/or decreasing wind intensities) during the one and the same interglacial highstand shortly after the 5e or 7 transgression maximum or whether they were deposited during the much younger sea-level sub-highstands, e.g. 5c, 5a or 7c, or 7a.