Aq. solns. of a corn. vinylpyrrolidone/methacrylamide/vinylimidazole/vinylimidazole methylsulfate copolymer were studied for lubricating properties by using a 4-ball tester. The friction coeff. and wear scar diam. decreased substantially with increasing concn. of the ammonium salt soln. In presence of the ammonium salt, the mech. system did not undergo seizure even at a load of 4 kN, whereas a seizure was obsd. for water already at 2 kN.