Most industries have a need for quality instruments for measuring concentrations and particle size distributions. The COULTER Counter is such an instrument and can examine particles one by one at rates up to 3000/sec. Sample particles are suspended in a conductive liquid such as saline. This suspension is rather dilute and is confined in a round-bottom beaker. Near-monosize reference microspheres of known diameter are used for calibration of the adjustable size threshold dial. Any given calibration procedure takes about 5 min. The quality of any particle size analysis result is greatly influenced by the accuracy and reproducibility of the sampling technique and by the accuracy and reproducibility of the sample dispersing technique. Because of its simplicity and speed, this device has proven to be a great asset when studies of sampling and dispersing are undertaken. A complimentary instrument is available for examining particle systems down to 0.01 µm. This device reads out the average particle size and a polydispersity factor.