Variants of mouse lymphocytic leukemia L1210 cells that overexpress P-gp due to either selection with vincristine (R) or transfection with a human gene encoding P-gp (T) are considerably less sensitive to repeated culturing in media containing sublethal concentrations of tunicamycin than parental L1210 cells (S) [33]. The gene discussed is PGP; the disease is lymphoid leukemia.