The first detailed deep seismic refraction study in the Bransfield Strait, West Antarctica, using sensitive OBSs (ocean bottom seismographs) was carried out successfully during the Antarctic summer of 1990/1991. The experiment focused on the deep crustal structure beneath the axis of the Bransfield Rift. Seismic profile DSS-20 was located exactly in the Bransfield Trough, which is suspected to be a young rift system. Alone the profile, five OBSs were deployed at spacings of 50-70 km. 51 shots were fired along the 310 km profile. This paper gives the first presentation of the results, A detailed model of the crustal structure was obtained by modelling the observed traveltimes and amplitudes using a 2-D ray-tracing technique, The uppermost (sedimentary?) cover, with velocities of 2.0-5.5 km s(-1), reaches a depth of up to 8 km. Below this, a complex with velocities of 6.4-6.8 km s(-1) is observed. The presence of a high-velocity body, with V-p=7.3-7.7 km s(-1), was detected in the 14-32 km depth range in the central part of the profile. These inhomogeneities can be interpreted as a stage of backarc spreading and stretching of the continental crust, coinciding with the Deception-Bridgeman volcanic line. Velocities oi. 8.1 km s(-1), characteristic of the Moho, are observed along the profile at a depth of 30-32 km.