16 to 32 lb) were exposed to 20 combinations of five air temperatures (20, 24, 28, 32, and 36°C; 68, 75, 82, 90, and 97°F) by four air velocities (0.1, 0.5, 1.0, and 1.5 m/s; 20, 100, 200, 300 ft/min). An infrared thermal imager (0.06°C or 0.1°F sensitivity) was used to simultaneously quantify resting pattern and surface temperature (Ts) of the pigs. Three postural behavior indexes were examined to represent thermal comfort level of the pigs; namely, the ratio of occupied floor area (Ap) to total surface area of the pigs - index Ia , the ratio of Ap to its maximum theoretical value - index If , and Ap per 100 kg body weight - index Ap(100kg) . The pigs showed a common range of Ia = 0.20 to 0.24, If = 0.75 to 0.84, and Ts = 34.5 to 36.3°C (94.1 to 97.3°F) corresponding to their thermal neutral zone (TNZ). By comparison, Ap(100kg) of TNZ was largely affected by pig age or body weight. Ia and If can serve as quantitative measures for assessment and control of thermal comfort of the pigs. They will be useful in the logic development of a novel controller that assesses and controls the microenvironment based on the resting pattern of the pigs as opposed to air temperature only. For instance, the increment or decrement of temperature setpoint can be determined in proportion to the deviation of the measured behavioral index from its ideal or TN values. The effects of air velocity on the effective environmental temperature of the pigs also were demonstrated with the postural index data. I