Detailed measurements are reported of acoustic emission (AE) produced during theδ → α phase transformation in plutonium-gallium alloys. During thermal cycling, the number of AE signals produced decreased with each thermal cycle more rapidly than the amount of additional material transformed. Thus, some portion of the transformation does not produce detectable AE. The average amplitude of the signals produced during quenching was not appreciably dependent on gallium content or cooling cycle. The amplitude of the signals is greater for rapid cooling than for slow cooling. The AE behavior is consistent with an isothermal, nonthermoelastic martensitic transformation.