Provenance variations in turbidite deposits from DSDP Sites 299 and 301 in the Sea of Japan have been determined on the basis of petrographic and electron microprobe analyses of quartz and feldspar in the 34-74mu size interval. Site 299 receives most or all of its sediment in this size interval from central Japan via the Toyama Trough. Site 301 is located in the middle of the Sea of Japan and receives detritus from the main Asian continent as well as from the volcanic island arc. Reflecting different types of source rock, the sediments from the island arc (Site 299) contain less quartz, more feldspar, more plagioclase An >= 50, less alkali feldspar Or85-100 and a higher mean An content of the unaltered plagioclase grains (40.2% vs. 29.2%) than Site 301. At Site 299 the quartz/feldspar n < 1.54 ratio increases with depth below the sea floor. This may represent either increasing separation from the Asian continent or increasing volcanism and albitization on the island arc. There are no differences in the detritus in the 34-74 mu size interval in sand versus mud beds at site 299.