A chronic toxicity bioassay was conducted with the microcrustacean Artemia salina as the testing organism for the toxic organophosphate diazinon in order to determine if the species is an appropriate indicator of pollution in aquatic environments. Tests of animal exposure to different concentrations of the toxicant were performed for 24, 48 and 72 hours after larvae hatching. Registered mortality data was used to obtain the lethal dose 50 (LD50) of the organophosphate for each exposure time, considering the immobilization of A. salina larvae as the mortality parameter. The lethal concentration (LD50) in the same exposure times was calculated by evaluating morphological changes on the three initial stages of larval development. Both doses were determined by using probit statistical analysis. Results indicate greater dose-response exactitude after 24 hours of exposure to the toxicant. High sensitivity of the organism to the toxicant was determined, thus indicating that A. salina is an appropriate ecotoxicological bioindicator of aquatic environments polluted with pesticides, with the special consideration that this species is a natural resident of saline water bodies, and thus could be used to control pollution in these environments as a result of the unrestrained usage of such toxic substances.