The Giemsa-banded karyotypes were studied in slowly and rapidly growing transplantable Morris solid hepatomas and in their in vitro stabilized cell lines. In the slower-growing solid hepatoma 8999, all chromosomes of the normal rat complement were readily identifiable. In the rapidly growing solid hepatoma 3924A, the mitotic cells exhibited a range of 54 to 120 chromosomes/cell with a stem-line of 64. In this liver tumor, extensive structural rearrangements occurred. Twenty-four structurally abnormal chromosomes were identified, and the origin of eight of these was suggested. Of the structurally abnormal chromosomes, six occurred in sufficiently high frequency that they can be used as markers for the identification of hepatoma 3924A solid tumor. Structural rearrangements were observed for autosomes 1 to 13. The first three pairs of autosomes of the rat complement were frequently found in chromosomal rearrangements in 3924A tumor cells. The most striking abnormality was in the marker chromosome, designated M1, which has a long homogeneously staining region. The observation of such a homogeneously staining region in human tumors and in rat hepatomas suggests a tumor-specific occurrence of a homogeneously staining region. The presence of this alteration may be connected with the altered enzymic pattern of 3924A tumor.

In hepatoma 8999 in tissue culture, the normal rat chromosome complement was observed with some numerical alterations. The cultured hepatoma 3924A cells contain the three autosomal markers found in the in vivo tumor karyotype. New chromosomal arrangements in which chromosome 2 was preferentially involved occurred in this cell line.

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This investigation was supported by USPHS Grants CA-13526 and CA-05034.

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