This cell line was derived from the L5178 thymic lymphoma induced by methylcholanthrene in a DBA/2 mouse. The cells are resistant to X-rays, but sensitive to ultraviolet radiation, heat and some potential anti neoplastic drugs (e.g., cis-PAD). After 6 months to 3 years in culture, the line converts to an X-ray sensitive state. The X-ray sensitive L5178-S line was derived from this line.