Flow cytometric DNA content analysis, employing fluorescent stains that bind stoichiometrically to DNA, is widely used by researchers and clinicians to monitor cell growth kinetics and to detect abnormalities in nuclear DNA content in tumor cells. Measurement precision is critical because small differences in DNA content may be significant; plastic spheres and cell nuclei are used for instrument calibration and standardization. Preparative techniques must provide a uniformly stained sample representative of the cells or tissue under investigation; multiparameter gating may facilitate cell selection within samples. Flow cytometry of light scattering, surface or intracellular antigens, RNA, chromatin structure, and/or DNA synthesis may provide additional useful information about neoplastic cell behavior.