Two simple techniques were developed to demonstrate bactericidal activity of bacteriocins. Both were based on allowing a lawn of indicator strain to grow first, then exposing the lawn to bacteriocin-containing cell-free supernatants in a well cut in the seeded agar lawn or by inoculating the bacteriocin-producing strain onto the indicator lawn. Lysis of cells of the indicator strain resulted in a clear zone. These techniques may be adapted to test antimicrobial substances other than bacteriocins and to help to determine their modes of action.