A subsea coupling comprises a male coupler having a probe and a female coupler comprising a socket for the reception of the probe. The couplers each include a valve which is openable on mating of the couplers to provide communication with the socket. The socket includes a recess accommodating an annular seal for providing a radial seal between the probe and the socket. In one embodiment the leading edge of the probe includes at least one relief channel for allowing the escape of hydraulic fluid entrapped between the probe, the seal and the recess when the couplers are made up. There may be a stand-off ring disposed between one end of the recess and the inner side of the seal. In another embodiment the relief channel is provided in the socket.