Usually extracellular microelectrodes record the activity from several neurons. In order to quantify the activity of an individual neuron in the record some form of spike discrimination is required. This paper describes a window discriminator for the separation of multi-unit neuronal spike trains which will display simultaneously the recorded spike information and the time-amplitude window levels. The window levels are displayed and can be delayed to include any portion of the spike waveform either above or below the initial threshold level. Several instruments can be cascaded for multiple time-amplitude interrogations of the same spike class from a single electrode recording. The instrument utilizes inexpensive commercially available integrated circuits.