U.S.A.

Chromosome studies were done on 18 somatic hybrid cell lines produced by fusing cells of the mouse A 9 line with cells of the human Daudi lymphoblastoid line derived from a patient with Burkitt's lymphoma. The human chromosomes were identified by their quinacrine fluorescent banding patterns. In one hybrid line the human chromosomes were identified also by the centromeric heterochromatin staining technique. Every human chromosome was identified in one or more of the hybrid lines. Some lines were homogeneous in terms of their human chromosome content, while others were quite heterogeneous. Detailed analysis of the A 9 chromosomes in one hybrid line showed very few changes in comparison with the chromo-some constitution of the average A g cell