The combined effect of simultaneous application of heat treatments, low frequency ultrasound (20 kHz) at different amplitudes, on Aspergillus flavus and Penicillium digitatum spore viability suspended in laboratory broth formulated at different a(w) (0.99 or 0.95) and pH (5.5 or 3.0), with or without vanillin or potassium sorbate were evaluated. An ultrasonic horn (13 mm) was submerged into the broth, heat and ultrasound was continuously applied. Survival curves were obtained, and D and z values calculated. For aw 0.99, increasing ultrasound amplitude and reducing pH resulted in reduced D values. At constant a(w), D values decreased with pH reduction. At constant pH, D values were lower for a(w) 0,99 than for 0.95. In general, D values were lower for thermosonication treatments than for thermal treatments. When potassium sorbate or vanillin was added and thermosonication treatment was applied at increased amplitude, lower D values were obtained. (C) 2004 Elsevier Ltd. All rights reserved.