Abstract: Disclosed is an abnormal pulse detector for use with a particle analyzing apparatus of the Coulter.RTM. type for generating discrete particle pulses in response to liquid suspended particles passing through a sensing aperture, the abnormal pulse detector comprising: a bad pulse detector for generating a bad count pulse for each of the particle pulses which have a width that is either too long or too short, comparative pulse detector means for generating a comparative count pulse for each of the particle pulses or for each of the particle pulses not generating a bad count pulse, counter and comparator circuitry for counting the bad count pulses and the comparative count pulses and for obtaining the ratio of the bad count pulses to the comparative count pulses so as to indicate a alarm condition when the ratio reaches a predetermined, unacceptable level.