Surface wetting to cool broiler chickens (Ross . Ross male, 46 .3 d, 2.8 . 0.1 kg) was investigated under 18 acute thermal conditions formed by 3 . 2 . 3 factorial combinations of dry–bulb temperature (tdb) of 35.C, 38.C, and 41.C; dew–point temperature (tdp) of 19.4.C and 26.1.C; and air velocity (V) of 0.2, 0.7, and 1.2 m s–1. The synergistic effects of tdb and tdp were expressed in terms of vapor pressure deficit of the air (VPDair, kPa). Surface temperature of the cooled birds was 1.9.C to 2.5.C lower than that of their control counterparts. Core body temperature (tb) rise above the normal level for the cooled birds was 1.2.C, 1.6.C, and 1.7.C lower than that for the control birds at 35.C, 38.C, and 41.C, respectively. Increasing V tended to narrow the difference in tb between the cooled and the control broilers, 2.0.C, 1.4.C, and 1.2.C for V of 0.2, 0.7, and 1.2 m s–1, respectively. Increasing tdp from 19.4.C to 26.1.C produced only 0.2.C overall difference in tb. Results of this study demonstrate that surface wetting coupled with good air movement, as in the case of tunnel ventilation, is effective in relieving heat stress of the birds even under relatively humid conditions. The cooling water needs, expressed as spray interval at a nominal spray dosage of 22 mL bird–1 (SI22, min) and evaporation rate (ER, mL/min kg0.67), were optimized by relating the SI22 or ER to the thermal conditions: SI22 = 70.50 – 27.14 V – 4.84VPDair, and ER = –0.0471 + 0.1700 V + 0.0297VPDair.