Differentiation of preferentially staining heterochromatic segments was achieved in somatic chromosomes of five monocotyledoneous species, when acetic-ethanol fixed meristems were subjected to 0.1 or 0.2 N HCl at temperatures between 60° and 80 °C, and stained with aceto-carmine. Suitable incubation time was temperature dependent and afforded 30 to 5 minutes. Several variations of the procedure were tested. The following plants were investigated:Allium cepa, A. flavum, A. carinatum, Scilla Sibirica, Fritillaria meleagris. InAllium carinatum besides heavily staining bands there appearently exist also bands even more labile against the HCl-treatment than euchromatin. The banding patterns do not reveal in all the species mentioned the total heterochromatin present in the form of chromocenters in the interphase nuclei, and do not always coincide with preferentially Giemsastaining segments as found by previous authors. The technique presented here and its variations seem to be a valuable and simple instrument for recognition and discrimination of heterochromatin. With the aid of these methods a high degree of structural heterozygosity was stated inAllium carinatum, A. flavum, andScilla sibirica. For the resp. heavily and weakly staining bands the abbreviations “Hy+bands” and “Hy−bands” are suggested.