Several plasmids were detected in the Gram-positive halophilic eubacteriumMarinococcus halophilusand in the related strain M52. The complete nucleotide sequence (3874 bp) of one of these plasmids, pPL1, was determined. Four major open reading frames were identified. Whereasorf3andorf4showed no sequence similarities to known proteins,repdisplayed a high sequence similarity to replication proteins of rolling circle plasmids. Upstream of this ORF, a sequence resembling the double-strand origin was detected. A region probably constituting the single-strand origin was identified. The ORFmobshowed sequence similarity with Mob proteins of rolling circle plasmids. The observed characteristics suggest that pPL1 replicates according to the rolling circle mechanism.