Beef patties (86 and 143 g) formed from high-fat (20 to 29%) and low-fat (6 to 10%) ground beef obtained in eight different selections for both high and low fat content were cooked by either a gas grill or an electric griddle. Patties were cooked to either 66.1 or 68.3 degrees C as determined in the thickest section, and internal temperatures were recorded after cooking at 1-s intervals for 180 s in both thick and thin sections of patties. Time-temperature curves (after cooking) were evaluated for compliance with regulatory requirements for classifying patties as fully cooked. For patties cooked to 66.1 degrees C, the maximum highest temperature in the thickest patty section often did not reach 71.1 degrees C (recommended for cooking of beef patties by consumers). Although thin sections of patties had higher temperatures than thick sections at the termination of cooking, temperature variability was greater and declines in temperature occurred sooner in thin patty sections. Failure to meet fully cooked, time-temperature requirements was greater in thin than thick sections. Thicker (143-g) patties possessed longer postcooking times before declining in temperature than thinner (86-g) patties. Although many beef patties cooked in this study achieved regulatory time requirements for maintaining 66.1 or 68.3 degrees C (as well as attaining 71.1 degrees C), some patties did not meet these requirements. Because of the considerable temperature variability that can exist within patties at the conclusion of cooking, use of end point temperatures of less than 71.1 degrees C is not recommended for consumers. Consumers should allow several minutes of holding following cooking before consumption to maximize the increases in postcooking temperature. Further research is required to establish cooking procedures that will improve temperature uniformity and eliminate "cold spots" during cooking of beef patties.