Previous investigations using several species of invertebrates have indicated a correlation between nuclear chromocentre content and the ability to regenerate. Such findings have resulted in the formulation of the hypothesis that the ability to regenerate may be dependent on cellular heterochromatin content. In order to test this concept further, a number of additional invertebrates were stained for heterochromatin (nuclear chromocentres). In accordance with the hypothesis, each species tested was found to contain numerous chromocentres. Many chromocentres were also found in cells of several vertebrates capable of partial regeneration, thereby extending the hypothesis to vertebrate regeneration. These findings provide additional supporting evidence for a correlation between cellular heterochromatin and the ability to regenerate.