Surface wetting to cool broiler chickens (46±3 d, 2.8± 0.1 kg) was investigated under 18 acute thermal conditions formed by three dry-bulb temperatures (tdb, 35, 38, and 41 oC) × two dew-point temperatures (tdp,19.4 and 26.1oC) × three air velocity (V, 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). Surface temperature of the cooled birds was 1.9-2.5 oC lower than that of their control counterparts. Core body temperature (tb) rise of the cooled birds was 1.2, 1.6, and 1.7 oC lower than that of the control birds at 35, 38, and 41 oC, respectively. Increasing V narrowed the difference in tb between the cooled and the control broilers, 2.0, 1.4, and 1.2 oC for V of 0.2, 0.7, and 1.2 m ·s-1, respectively. Increasing tdp from 19.4 to 26.1 oC produced only 0.2 oC 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, of the form, SI22 = 70.50 – 27.14 . V – 4.84 .VPDair, and ER = - 0.0471 + 0.1700 . V + 0.0297 .VPDair.