To elucidate how the brain processes information, the functioning of neuronal networks has to be analysed. We developed a multi-neuron recording system that is able (1) to record several neurons with one multi-unit microelectrode, (2) to separate the multi-unit data into single-unit spike trains and (3) to display the neuronal activity, especially the interactions between the different single units, in real-time. The system consists of two PDP-11/73 laboratory computers, each extended with a TMS-32010 based TZQ-11 coprocessor. One computer is programmed to detect and classify spikes from the electrode signal. The second computer does further data processing and controls the experimental procedure (Generation of stimuli etc.).