High-power pulsed microwave fluences interact with aqueous solutions in a complex way. The incident energy partitions into direct heating (generally on the side facing the source) and an acoustic wave transient (the so-called microwave acoustic effect) which may dissipate thermal energy differently based on absorber geometry and acoustic wave interference. In a search for chemiluminescent (imaging) dosimeters suitable for distinguishing direct heating and acoustic wave phenomena, we found that dilute solutions of diazotized luminol produce a reliable 200-fold luminescence increase above the quiescent condition when 115 ml of the solution is subjected to 62 W of 20-kHz acoustic energy. The contrast ratio (irradiated to quiescent) is markedly diminished and irreproducibility is introduced if carbon dioxide is not thoroughly excluded from the dosimeter solution by bubbling with nitrogen gas before use. Dissolved carbon dioxide acts mainly to increase quiescent thermochemiluminescence. The ratio is largest if the dosimeter solution is chilled to 0ΠC. The contrast ratio is pH dependent and maximum between pH 7 and 7.5, and sonochemiluminescence generated in this manner fades with a time constant of about 0.5 s when the irradiation is stopped. The light output from this dosimeter is well above the sonoluminescence produced in pure water under the same irradiation conditions.