Three different fluorochromes were tested for their ability to label the plasma membrane proteins of neutrophils without labelling intracellular structures. A fluorescence quenching technique was used to differentiate between extra- and intracellularly localized fluorescence. Fluorescamin and fluoresceinisothiocyanate were shown to stain intracellular structures as well as the plasma membranes of the cells. Another fluorochrome, Evans Blue, is proposed since this dye was shown, by using the fluorescence quenching technique, to selectively stain the plasma membrane of viable neutrophils.