The intercalation of the corresponding product in the DNA molecule is related to activity of some anti-neoplastic antibiotics, and to chemical carcinogenesis and mutagenesis. DNA-intercalating agents may inhibit replication and/or transcription, and stop cell proliferation. This work deals with the mechanisms of staining and fluorescence, and with the intercalative binding of some cationic dyes. It is shown that chromatin fluorescence depends on the product concentration, it is not modified by nitrites, molibdate or inorganic cations, but it is inhibited by non-fluorescent intercalating substances such as caffeine and o-phenanthroline. The results suggest the existence of intercalative binding. Contrarily, chromatin staining is related to electrostatic binding with DNA.