Nucleate pool boiling heat transfer coefficients of ammonia/water mixtures were measured at a pressure of 0.4 MPa on a horizontal heated fine wire having a diameter of 0.3 mm. The nucleate pool boiling aspects were observed, after the addition of a surface-active agent to the mixtures. The effects of the concentrations of ammonia and the surface-active agent on the coefficients were clarified experimentally for the ammonia fraction range 0.1 <= C <= 0.9 and surfactant concentration range 0 <= C-s <= 3500 ppm. The results showed that the coefficients were enhanced at C <= 0.5 and in low heat flux ranges just after the onset of boiling. It was also found that the enhancement effect caused by the surfactant disappeared at surfactant concentrations of more than 1000 or 1500 ppm. (C) 2012 Elsevier Ltd. All rights reserved.