Most human cancers are associated with abnormal (marker) chromosomes. In past and present studies banding analysis have uncovered a much larger number of markers in cancer cells than was seen with standard (Giemsa) staining. Furthermore, common markers of identical morphology and origin were found in tumors of related or unrelated tissues or organs, suggesting that in all probability such markers, although present in cancers of diverse nature, may indicate a common etiology, either related to the causation of the cancers, to the progression of the tumors, or to the predilection of certain chromosomes to undergo morphologic changes leading to marker formation. Even though some markers were common to different tumors, the bulk of the markers in the cancers studied could not be identified with certainty and their nature varied from tumor to tumor.