The autoinduction and glucose repression of luciferase synthesis in batch cultures and continuous cultures of Vibrio fischeri were investigate. As previously reported, a lag in luciferase synthesis occurred in glycerol-grown batch cultures and addition of d-glucose to the medium extended the lag period. A phosphate-limited chemostat culture with d-glucose as energy source (specific growth rate, μ=0.45 h-1) contained uninduced levels of luciferase. Luciferase activity increased to an induced level upon addition of c-AMP or autoinducer to such a chemostat culture while cell mass remained constant. Furthermore, when μ of a phosphate-limited chemostat culture containing d-glucose as energy source was decreased from 0.45 to 0.30 h-1, luciferase activity increased from an uniduced to induced level. After exogenously added c-AMP or autoinducer was diluted out of a phosphate-limited continous culture or after μ was increased to 0.45 h-1, luciferase activity remained at an induced level. Apparently, luciferase in V. fischeri was subject to a catabolite repression by d-glucose that could be overridden by autoinduction or by an autogenous control element.