The chromosomes obtained by culturing lymphocytes from blood samples of the long-finned pilot whale Globicephala melaena, were studied by Q- and C-banding. The culture method was very difficult to handle. The karyotype of the long-finned pilot whale has a typical cetacean 2n = 44 chromosome number. The O-band revealed a characteristic banding pattern, which showed a heteromorphism between individuals but not within individuals. These observations were supported by the C-banding, which disclosed clear size variation of heterochromatin in some chromosome pairs. A species specific C-band pattern was observed in comparison between Globicephala melaena and Globicephala macrorhynchus, the short-finned pilot whale. O- and C-band markers can be used in family- and population studies if a good technical quality can be achieved. The finding of an inactivation of one of the X-chromosomes in females opens the possibility of using the method of staining the sex chromatin to determine the sex of small foetuses (