Dense copepod scattering layers were detected in the upper 50 m of the water column in the Bering Sea north of the western Aleutian Islands during June 1992. Acoustic data were collected at frequencies of 200 and 420 kHz, and compared with simultaneous estimates of wet weight biomass from net tows. Regression of net and acousticdata produced a scaling factor of −69.6 dB g−1 to convert volume scattering to biomass. Application of the fluid sphere scattering model produced an average equivalent spherical radius for the targets of 0.54 mm. The major sound-scattering organism, Neocalanus cristatus copepodid stage V, dominated the biomass in the pycnocline between the upper mixed layer and the underlying cold intermediate layer. Populations were dominated by Neocalanus plumchrus and Neocalanus flemingeri,with greatest abundance above the pycnocline.