Perturbation analysis is used to obtain expressions for the harmonic content of finite‐amplitude waves propagated in a relaxing liquid. Comparison is made with similar expressions for the nonrelaxing case. Experimental measurements were made with 2.57‐MHz rf pulses in a 0.2‐Maqueous solution ofMnSO4to test the theoretical results. Agreement is excellent for the fundamental frequency. The second‐harmonic curves have the correct shape but are 10% 15% smaller in absolute magnitude.