A transformation assay was used to assay the amount of DNA present in the extracellular medium of a growing culture of Acinetobacter calcoaceticus. It was observed that small amounts of DNA were liberated during the entire exponential growth phase in a batch culture. Release of DNA could be fully accounted for by lysis of cells. Lysis was quantified via simultaneous measurement of beta-galactosidase activity of cells and supernatant, with a strain that contained a plasmid (pAPA100) with lacZ under control of a constitutive beta-lactamase promoter. In conclusion, no evidence could be obtained indicating that Acinetobacter calcoaceticus actively excretes DNA, to be used for DNA exchange.