At 25 degrees C the ultrasonic absorption coefficient of aqueous solutions of triethylenediamine (TED) has been measured as a function of frequency v (200 kHz less than or equal to v less than or equal to 4.6 GHz) and solute concentration c (0.0025 mol/L less than or equal to c less than or equal to 2.56 mol/L). One solution has also been studied at 15 degrees C and 35 degrees C. To look for the dependence upon the pH some spectra have been recorded with NaOH or HCl added. The measured spectra have been analyzed in terms of a model relaxation function containing a Debye relaxation term and a term that represents noncritical fluctuations in the concentration. The Debye term is related to the protolysis of the TED molecule. Depending on the pH either the first or the second step of protonization of TED is reflected by the relaxation process. The forward and reverse reaction rates and the isentropic reaction volume have been determined from the relaxation parameters and it has been found that the amplitude and relaxation time of the Debye term can be described by one set of activity coefficients for the first protolysis reaction. The noncritical concentration fluctuations are analytically represented by an extended version of the Romanov-Solov'ev theory that also considers spatial correlations. At c > 0.5 mol/L a correlation length of about 4 Angstrom is found. The finding of TED association at an elevated solute content is consistent with previous results from dielectric spectrometry.