Two potent stimulators of uterine contraction, the diterpenes kaurenoic and grandiflorenic acids, were isolated from leaves of Aspilia mossambicensis. Their presence supports a hypothesis that wild chimpanzees consume Aspilia species for their pharmacological properties and may explain why female chimpanzees consume Aspilia leaves more frequently than do males. Thiarubrines were not present in any of the leaf samples collected in Mahale or Gombe National Parks, Tanzania, although these antifungal and nematocidal dithianes were found in significant amounts in roots.