We describe a method for continuous cultivation of microorganisms utilizing liquid or gaseous water insoluble substrates as a single source of carbon and energy. The water insoluble substrate, which is also the growth-limiting factor, enters the cultivation space as a manually adjustable single-compound material flow. All nonlimiting nutrients (with the exception of oxygen) enter the cultivation space as ingredients of titrant solution which feed rate is reliably coupled to the rate of substrate addition by means of the system titrator.The method provides mild starting conditions appropriate for primary isolation of microorganisms utilizing substrates with growth-inhibiting properties such as BTEX (benzene, toluene, ethylbenzene, and xylene). The sound control over the microbial specific growth rate makes it suitable for precise kinetic studies as well.We provide a detailed description of both the principles of the method and the equipment used. The dependence of the systems operative range on the concentration of titrant solution is illustrated in the case of continuous cultivation of a mixed bacterial culture on toluene. (C) 2003 Wiley Periodicals, Inc.