Six hepatomas, each induced in a different strain-2 guinea pig, were studied. Four of the six tumors were different in histologic appearance, transplantability, and chromosomal constitution. Two of the six tumors (lines 1 and 8) were similar in these characteristics. During transplantation of one of the tumors (line 7 in the ascites form), a subline arose that differed from line 7 in histologic appearance, transplantability, and chromosomal constitution. This subline (7B) was biologically similar to lines 1 and 8.