Results from the hydro-acoustic studies aiming at evaluation of the Euphausia superba biomass in the Bransfield Strait in March 1981 are presented. These investigations, called conventionally Micro-FIBEX, were carried out on the r/v "Profesor Siedlecki" during 13-16 .March 1981, as continuation of the studies carried out in that region within the scheme of the FIBEX programme in the period of 5-12 March 1981. The abundance of the biomass was estimated at 258 thousand ton, which at the investigated area of about 1755 NM2 gives the mean value of biomass density 142 t/NM2 (41.4 g/m2).