The applications of computers and microcomputers in particular interfaced to bench-top bioreactors are briefly discussed. Compact, quick-access microcomputers (e.g., desk-top calculators) offer the possibility of on-line data acquisition and analysis as well as process control (sequencing, interactive control) with relatively high efficiency at reasonably low costs of installation in laboratory experiments. The configuration of such a computerized system is described in detail along with the capabilities and features of interfacing hardware components. The limits in applicability due to slow operating speeds of fully developed microcomputer systems in particular are pointed out and a survey on investment costs for high-performance, compact desk-top calculators and some peripheral devices is given. Examples of on-line acquisition of several directly accessible environmental process parameters and computations of directly inaccessible state variables are presented in the form of type-writer print-outs. The advantages of on-line experiments for establishing sophisticated control algorithms and for studying the physiological behaviour of the microbial population are demonstrated.