Three different types of toxicological test were conducted, viz. the standard toxicological test at varying pH, a test with starved larvae and a test with different ionic composition of the water. For the larvae of L. sponsa, ammonia toxicity was examined only in the standard test at one pH value and in the test with varying ionic composition of the medium. Total ammonia was more toxic at elevated than at low pH to both S. flaveolum and E. najas larvae. In contrast, toxicity based on the un-ionized form appeared to increase with decrease in pH value. In general, larvae of all spp. have a high ammonia tolerance when compared to other aquatic animals. Tests with starved larvae showed that the ammonia tolerance of starved larvae of S. flaveolum was 3.7 times greater than that for the fed ones; for E. najas, this difference was only 1.2 times, explanations of this effect are discussed. Tests in varying ionic composition of the water illustrated that the absence of sodium ions accounts for a considerable increase in ammonia toxicity. It is interesting that a similar trend was found for fishes and crustaceans. Mechanistic explanations, which may differ from that for other groups, are proposed. Odon. larvae seem to be unsuitable for the bioindication of ammonia pollution.