Some types of acridine derivative and especially Quinacrine dihydrochloride and its mustard may be successfully used as chromosome marker and to investigate the chemical differentiation of euchromatin and heterochromatin. — There are at least four main types of heterochromatin, showing all possible combinations of positive and negative cold effect “starvation” (St. + or St. -) and enhanced or reduced fluorescence (Fl. + or Fl. -). —The relationship between the four different classes of heterochromatin is not yet clear.