The aim of this study was to assess the acute toxicity of phenanthrene, pyrene and benzo[a]pyrene using fur-marked bacterial biosensors. Standard solutions of phenanthrene, pyrene and benzo[a]pyrene were produced using 50 mM hydroxpropyl cyclodextrin (HPCD) solution. Four microorganisms containing the lux cassette were used as the test biosensors and over the incubation time period (280 min), there was no significant decrease in bioluminescence in any of the biosensors. This study has shown that the three PAHs tested are not acutely toxic to the prokaryotic biosensors, although acute toxicity has been shown in other bioassays. These results question the rationale for using prokaryote biosensors to assess the toxicity of hydrophobic compounds, such as PAHs, from more complex environmental matrices.}