Acoustic backscatter measurements were conducted on a stationary harbor porpoise (Phocoena phocoena) under controlled conditions. The measurements were made with the porpoise in the broadside aspect using three different types of signals as follows: (1) a 475-ms linear frequency-modulated (FM) pulse with a frequency range from 23 to 160 kHz; (2) a simulated bottlenose dolphin (Tursiops truncates) click with a peak frequency of 120 kHz; and (3) a simulated killer whale (Orcinus orca) click with a peak frequency of 60 kHz. The measurement with the FM pulse indicated that the mean target strength at the broadside aspect decreased from -26 dB to -50 dB as the frequency increased from 23 to 120 kHz in a nearly linear fashion (on a logarithm plot) and dropped rapidly by 27 dB to -77 dB at 150 kHz. Target strength variation with the frequency was similar to that in a previous backscatter measurement performed on a bottlenose dolphin over a similar frequency range (23–80 kHz). The target strength of the smaller harbor porpoise was about 15–16 dB lower than that of the bottlenose dolphin. The difference in the lung volume of the two species when expressed in dB was also approximately 15 dB. The results suggest that the dolphin bubbrt had broadband anechoic properties.