The commercial penaeid prawns of northern Australia have been surveyed by electrophoretic techniques to determine the extent of geographic differentiation throughout their ranges in Australian waters. Genetic differences were detected among widely separated populations of P. latisulcatus and M. endeavouri, but P. esculentus, M. ensis, P, semisulcarus and P. merguiensis showed no evidence of genetic differentiation. In both P. latisulcatus and M.endeavouri the most marked differences were detected between the samples from the Gulf of Carpentaria and Western Australia. The measures of genetic divergence between these two regions are Φ* = 0.127 for P. latisulatus and 0.214 for M. endeavouri.