GSHE1cell cultures were established from 13-day-gestation fetuses collected aseptically by cesarian section from inbred Syrian hamsters, strain LSH/ssLAK (Lakeview Hamster Col ony, Nuffield, N. J.). Pools of primary cultures from littermates were stored in liquid nitrogen. Secondary cultures were initi

was induced by carcinogen treatment. Many cell types in culture undergo a process of neoplastic transformation spon taneously, i.e., in the absence of a known carcinogenic insult (31). During this transformation process, aneuploid cell lines arise that are often nontumorigenic in animals when injected as a cell suspension. These lines are generally termed “nor mal' â€ãnd are frequently used as model systems to study chemically and virally induced carcinogenesis (8). In this report, I present evidence that spontaneous neoplastic transformation of Syrian hamster embryo cells in culture occurs in at least 2 steps. An intermediate stage is represented by an aneuploid cell line. These cells differ from the normal, diploid cells, and evidence is presented that these cells are preneo plastic.