A cell clone, P3, from a human teratocarcinoma cell line was isolated and characterized for use as targets in mutagenesis studies to identify potential carcinogens and elucidate the genetic events most likely to result in malignant transformation. Human breast carcinoma BJ cells were incorporated into the P3 system to supply the necessary enzymes for chemical activation. 51 references, 3 figures, 3 tables. (ACR)