Radiocarbon dating of marsh peats in south-central Louisiana permits interpretations of relationships between former positions of land and sea. Past marsh surfaces, now buried at depths ranging from 4 to 40 feet, indicate the positive change in level that has taken place since their origin. Abundant evidence for a stillstand in sea level during the past 2000–5000 years affords a fixed datum for differentiation between eustatic sea-level rise and subsidence. The rate of subsidence in the study area is 0.24 foot per century. Results show a eustatic sea-level rise of approximately 23 feet in the interval between 7000 and 3650 years B. P. when stillstand was reached. There is no indication that sea level was higher than at present at any time during the interval studied.