Since 1982 when secondary. poisoning of Red-tailed Hawks (Buteo jamaicensis) was documented following the recommended use of famphur on cattle, the Patuxent Wildlife Research Center has tested for organophosphate (OP) poisoning in selected birds of prey found dead. This report documents the circumstances for a number of. cases where birds of prey were killed by OP pesticides in the United States. Many of the cases were brought to our attention by the U S. Fish and Wildlife Service Division of Law Enforcement The cases may be divided into three categories: misuse, approved use, and unknown. Now that we are looking for OP poisoning of birds of prey, we are finding it more frequently than previously suspected.