Thermal inactivation of a four-strain mixture of E. coli O157:H7 was determined in 90% lean ground beef, and lean ground chicken. Inoculated meat was packaged in bags which were completely immersed in a circulating water bath and held at 55, 57.5, 60, 62.5, and 65 degrees C for predetermined lengths of time. D-values, determined by linear regression, in beef were 21.13, 4.95, 3.17, 0.93 and 0.39 min, respectively (z = 6.0 degrees C). Using a survival model for non-linear survival curves, D-values in beef ranged from 20.45 min (D1; and there was no D2) at 55 degrees C to 0.16 min (D1) and 1.45 min (D2) at 65 degrees C. When E. coli O157:H7 four-strain cocktail was heated in chicken, D-values calculated by both approaches were consistently less at all temperatures. The heat resistance of E. coli O157:H7 was not altered after refrigerated or frozen storage of inoculated beef for 48 h. The results of this study will be beneficial to the food industry in designing HACCP plans to effectively eliminate E. coli O157:H7 in the meat products used in this study.