The importation and release of non-indigenous organisms to control pest populations continues to be promoted as environmentally safe; however, accumulating evidence from past and current projects raises serious concerns. Biological control technology using non-indigenous agents is as highly unnatural and anthropocentric as is the use of chemical pesticides and should be recognized as an artificial rather than a natural biocontrol. Introduced biocontrol agents have been implicated in the extinction of numerous nontarget species, disrupted native ecosystems, and harmed human welfare. Of greatest concern to conservation are species extinctions, including numerous species of land snails, insects, birds, and reptiles. Environmental harm is best documented on islands, but severe negative impacts also occur in continental areas. Many effects were discovered serendipitously by persons conducting fieldwork at the right time and place, thus many additional severe impacts certainly escaped notice and remain undocumented. Persons who release organisms beyond their natural range undertake a grave responsibility. Once released these agents may be pervasive (i.e., able to disperse far beyond the target system), permanent (i.e., able to multiply and evolve in perpetuity), injurious (i.e., able to harm nontarget organisms), and insidious (i.e., able to affect ecosystems, sometimes in profound ways). Long-term ecological studies are needed on both the efficacy and environmental impacts of biocontrol introductions to make applied ecology more predictive and to produce more appropriate protocols governing proposed introductions. Given the risks, more open public over-sight and more comprehensive regulation of all proposals to introduce and release non-indigenous organisms are required.