A technique for Acridine Orange staining of cells for automated flow analysis involving post-staining fixation with Millonig''s glutaraldehyde buffer is presented. Preliminary data indicate that with this protocol there is decreased background fluorescence and increased signal to noise ratio in flow. Stained cells may be stored for several months without alteration in cellular morphology or fluorescence characteristics. Nuclear and cytoplasmic fluorescence did not appear to vary significantly with respect to cell concentration or distribution on a slide or filter when cells are stained according to the glutaraldehyde protocol. [Human cervical scrape specimens were used in this study.].