The terms “competition” and “allelopathy” should be used in ways consistent with some set of criteria, perhaps those proposed in this discussion. Proposed proof of competitive interference includes: (1) identification of the symptoms of interference; (2) demonstration that the presence of the agent is correlated with reduced utilization of resources by the suscept; (3) demonstration of which resource(s) depleted by the agent are limiting resources; and (4) simulation of that interference (in the absence of the agent) by reduction of the supply of resources to levels that occur during interference. Proposed proof of allelopathic interference includes: (1) identification of the symptoms of interference; (2) isolation, assay, characterization, and synthesis of the toxin; (3) simulation of the interference by supplying the toxin as it is supplied in nature; and (4) quantification of the release, movement, and uptake of the toxin. It would be desirable but not essential to show that the selectivity of the toxin to various species corresponds to the range of species affected by the allelopathic agent. We propose that fulfillment of the above criteria would constitute proof of competitive or allelopathic interference. According to these criteria, it is possible that neither competitive nor allelopathic interference has been unequivocally proven at the present time. These criteria are proposed as a basis for evaluation of experimental evidence and as an indicator of deficiencies in our technology.