The island of Borneo is one of the oldest known —and least reported on—sources of diamonds. Although diamond mining historically was concentrated in the western area of what is now Kalimantan, recent activity has focused on the alluvial deposits in the southeast. A progress report on the first bulk sample pit in this area found that significant amounts of diamonds appear to be concentrated beneath the center of the Danau Seran swamp. The traditional hand-mining methods contrast greatly with the sophisticated techniques used to mine the first bulk sample pit. Virtually all of the diamonds recovered are gem quality, although most are relatively small, averaging about 0.30 ct. Future potential for southeastern Kalimantan appears excellent.