Technical Abstract: A continuous flow apparatus was developed to measure thermal resistance (D and z values) of microorganisms at temperatures above 65°C. This apparatus was originally designed to test if vegetative microorganisms exhibited unusually high thermal resistance that prevented them from being completely eliminated at temperatures (116-157°C) applicable to the vacuum-steam-vacuum processes. The apparatus was composed of a HPLC pump, a heating unit, and a cooling unit. It was designed to measure very small D values (< 1 s). Three randomly selected organisms, Listeria monocytogenes, Salmonella Heidelberg, and Escherichia coli O157:H7 in de-ionized water, were tested in the continuous apparatus at temperatures ranging from 60-80°C. Studies showed that the D values of these organisms ranged from 0.05-20 s. Heating at 80°C was found basically the physical limit of the system. Experimental results showed that L. monocytogenes, S. Heidelberg, and E. coli O157:H7 did not exhibit unusual heat resistance. The conditions used in the VSV processes should have completely eliminated organisms such as L. monocytogenes, S. Heidelberg, and E. coli O157:H7 if present on food surfaces. The incomplete destruction of bacteria during VSV may be attributed to that the surface temperatures are below the steam temperatures and that bacteria are hidden underneath the surface.