Tropical biologists are often frustrated in their attempts to study plants, animals, and climate in the forest canopy because of the difficulty of access to this region 20-50 meters high. This problem can be overcome by the use of free-standing towers (Pasoh, Malaya; Barro Colorado Island, Panama) or by tree platforms (Ulu Gombak, Malaya). In April, 1978, we constructed a canopy platform and ladder at our study site in the Kutai Nature Reserve, East Kalimantan, Indonesia, to collect data on forest phenology and the travel paths of arboreal birds and mammals. Since our 39 meter-high platform and ladder are economical to construct and safe to use (desirable features) we describe its construction here in more detail. We selected a large (180 cm dbh) Shorea situated on a sloping ridgetop so that the platform commands a view over the forest downslope and into the crowns of trees upslope. This tree has 32 meters of clear bole to where it divides into two large ascending secondary trunks. Access to the crown was gained by having one of our Indonesian assistants climb a smaller adjacent tree, cut off its crown, and shoot a nylon line over the lowest limb of the Shorea using a slingshot. This nylon line was then replaced with a 9 mm climbing rope. Both ends were tied to a tree near the ground.