A coincidence counting apparatus of high resolution is described. It employs proportional counters whose amplified pulses trigger blocking‐oscillators to give artificial pulses which are used in the coincidence discriminator. A continuously variable time delay is provided in one of the amplifier channels for determining the resolving time and for studying delayed coincidences. Under favorable conditions the passage of an ionizing particle through a counter can be determined to within an uncertainty of about 10−8sec.