The design and performance characteristics of a small volume (20 ml) continuous culture device for the cultivation of luminous bacteria are described. This simply constructed device can be used to supply luminescent bacteria with constant properties for either laboratory use or the assay of environmental pollutants. Furthermore, bacteria can be deployed to make sensitive (<1 nM) oxygen measurements. The culture device may be configured, alone or in combination, as a chemostat, turbidostat or a "bioluminostat" where bacterial bioluminescence becomes the controlling variable. Over extended periods (>1 week) it was possible to maintain steady-state luminescence within 5% of a pre-set value, although occasionally a non-bioluminescent "mutant" became dominant; in this case light emission was irreversibly lost. A secondary chamber provided additional flexibility and easy manipulation of the cultivated bacteria for testing. The continuous culture system is also suitable for the growth of recombinant microorganisms that either constitutively express luciferase, or do so in response to stress promoter activity. The non-standard control methodologies reported may have important research and industrial applications, for example in providing immediate process control or as an inferential method to optimize biomass: product yield ratios.