In this bioassay, the sublethal and lethal toxicity of the antipsychotic haloperidol was determined on the species L. minor and D. magna using five doses of haloperidol for 48h (0.22 mg·L-1, 0.67 mg·L-1, 2 mg·L-1, 6 mg·L-1 and 18 mg·L-1). The half maximal effective concentration (EC ) found in L. minor was 11.19 50 mg·L-1, while the no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) was 6 mg·L-1 and 18 mg·L-1, respectively. In the case of D. magna, the EC and mean lethal 50 concentration (CL ) was 29.82 y 290.55 mg·L-1 at 24h and 1.83 mg·L-1 y 5.69 mg·L-1 at 48h respectively. 50 The NOEC at 24h and 48h was 2 mg·L-1, and the LOEC was 6 mg·L- 1. L. minor and D. magna are considered bioindicators due to their sensitivity to haloperidol, so their exposure to this drug could affect and cause a risk to aquatic communities.