A major goal of this laboratory is to gain insight into the sequence of molecular and cellular changes which disturb the balance between growth and differentiation during chemical carcinogenesis (See also LEP projects Z01 CP-05276-02 and Z01 CP-05277-02). Several culture systems for normal cells of rodent and human derivation are being used to approach this goal. Human urothelium, mouse keratinocytes and hamster tracheal epithelium in conventional media all undergo squamous terminal differentiation and fail to multiply to a useful extent. To overcome this problem, defined media in which serum is replaced by growth factors have been used successfully in all these systems. In serum-free media substantial cell replication occurs; when switched to media containing serum or increased calcium levels, these cell systems undergo terminal differentiation. The efficacy of nutrient medium MCDB 402 is also being assessed in the mouse cell line BALB/3T3 cl A31-1-1, not only to obtain appropriate growth control of target cells for transformation studies, but also to provide a baseline for comparison of the growth response of normal and transformed cells.