The phytochemicals found in the fruit of the extremely rare Pleodendron costaricense, are reported. Both the peel and the pulp contain mixtures of oxygenated essential oils and drimane dialdehydes, which are known to have a variety of biological activities. The major constituent in the essential oil is ?-farnesene accounting for 75% of the essential oils in the pulp. Cinnamodial and mukaadial are the major dialdehydes found in the peel and pulp, respectively. The question of why capuchin monkeys bite into the fruit and rub the contents in the pulp on their fur but do not eat the fruit is addressed. The glycerides in the seeds consist of two unsaturated (oleic, 53.5%, and linoleic acid, 25.9%) and two saturated acids (palmitic, 14%, and stearic, 6.5%) acids. This work may help shed light on reasons why these trees are only very rarely reproducing naturally. #Dedicated to Luis Poveda Alvarez, and the memory of Pablo Sanchez Vindas, both outstanding botanists. They introduced us to the two Pleodendron costaricense trees growing in the mountains south of Parrita, Costa Rica