The alkylation repair deficient (Mer- phenotype) cells produce high levels of proteolytic enzyme plasminogen activator (PA) after treatment with alkylation agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Both, in Escherichia coli and in mammalian cells O6-methylguanine (O6-MeG) is repaired by analogues O6-methylguanine-DNA methyltransferase (MGMT). In E. coli MGMT is product of ada gene. To investigate the effect of bacterial MGMT expression on the induction of PA activity in human cells, we have transfected ada-alkB operon into Mer- human A1235 cells that are known to produce high levels of PA after MNNG treatment. We have shown here that A4 and A8 transformants that harbour ada gene become resistant to killing by MNNG. In addition, MNNG produced induction of extracellular PA activity was much less pronounced in A4 and A8 transformants (induction ratio 3.42 and 3.74, respectively) than in control A1235 and Aneo-1 cells (induction ratio 11.04 and 9.11, respectively). However, changes of intracellular PA activity were not significant. It appears, therefore, that induction of extracellular PA activity is inversely related to the cell capacity to repair the DNA lesions induced by alkylation agents.