Transport variations through the Korea-Tsushima Strait are examined from two lines of bottom-moored acoustic doppler current profilers (ADCPs) deployed southwest and northeast of Tsushima Island in May 1999. Almost full-depth velocity profiles are measured. An optimal interpolation (OI) scheme is used to interpolate the data spatially and to provide error estimates along each section. The strong northeastward current core through the southern section lies approximately in the center of the strait, and small southwestward flows occur sporadically near both the Korea and Japan coasts. Much of the flow through the northern line occurs near the Korea and Japan coasts, with a weak southwestward mean flow and large variability in the strait center on the leeside of Tsushima Island. The estimated mean transport is 2.9 sverdrups (Sv) through the southern line and 2.5 Sv through the northern line. The northern line does not extend close to the Korea coast where there is significant flow. Expected errors in the transport estimates at any time are about 0.5 Sv RMS for each mooring line. The gradual transport increase through the summer is carried through the center of the southern line and on the Korea side of the strait through the northern line. ¿ 2001 American Geophysical Union