The survival pattern and plasmid maintenance of Escherichia coli was examined in an artificial seawater microcosm. It was found that the three strains of E. coli (EK3C, H10407, and 34309) included in the study were able to maintain a portion of cells in the culturable phase for at least 3 years in artificial seawater. Along with retaining culturability, that portion of the cell population also maintained their indigenous plasmids over the 3-year period. It is concluded that cells of E. coli maintaining culturability in seawater are selectively adapted to the salinity of seawater, remaining in a culturable state. The results of the study are significant in that it has been assumed by many public health authorities that E. coli cannot survive, without nutrient addition, in seawater for long periods of time, i.e., years of exposure to seawater. (Copyright (c) 1993 Federation of European Microbiological Societies.)