On double-minutes and their origin in a benign human neoplasm, a mixed salivary gland tumour.

The cytogenetical observations in the first double-minute (DM)-positive benign neoplasm, a human pleomorphic adenoma, are described. It is suggested that in the present adenoma the first DM was formed from a structurally and/or functionally specialized segment of the long arm of a chromosome No 12. If so, the results also indicate a close relation between chromosome regions preferentially involved in structural rearrangements in a certain tumour type and chromosome regions with the potential capacity to become released and behave and function as DMs.