who first aroused interest in the chromosome constitution of tumour cells. On the basis of studies on abnormal chromosome segregation and the result-ing disturbances in the early larval development in dispermic fertilized sea urchin eggs, Boveri formulated the hypothesis that the malignancy of the mammalian somatic cell might be the result of a certain aberrant chromosome constitution". The early efforts to test this concept yielded no conclusive information, however, mainly on account of inade-quate methods.

During recent years critical facts have been collected by means of improved techniques about the chromosome cytology of various tumours. As a result discussion about the significance of aberrant chromo-some constitutions in cancer cells has been revived. Several investigators consider that karyotype instability is not essential for the acquirement of neoplastic properties". Others regard genetic variation at the chromosomal level as the cause of neoplastic trans-formation or at least indispensable for tumour progressionº. The view of the latter group is mainly based, however, on results from material which is not truly representative of primary tumours. With these opposing views in mind, karyotype analysis has been undertaken in some spontaneous tumours, virus-induced tumours, tumours caused by endocrine imbalance, and chemically induced primary tumours in various species including the domestic fowl, mouse, rat, Chinese hamster, domestic rabbit, cattle and man. The results obtained will be outlined.