To determine the endocrine effects of the treatment of organophosphate poisoning, this prospective study was conducted in a university-based emergency department among patients with a history and clinical findings compatible with those of organophosphate poisoning. Thyrotrophin (TSH), free triiodothyronine (FT3), free thyroxine (FT4), follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), progesterone (PRG), adrenocorticotropic hormone (ACTH), cortisol, and testosterone (TST) levels were analyzed before and after treatment with atropine and pralidoxime. The Wilcoxon's sign rank sum (non-parametric) test was used to compare dependent variables before and after treatment. A total of 44 patients (19 male; mean age: 28.5+/-12.6 y) were enrolled in the study. Patients were hospitalized for 5.4+/-1.3 days. Posttreatment ACTH, cortisol, PRL, FT3, FSH, and PRG levels were significantly lower than pretreatment levels (P<.05). The decrease in TSH, LH, and TST levels did not reach statistical significance, while FT4 levels increased following the treatment (P<.05). Six patients were diagnosed on admission with sick euthyroid syndrome, and I I patients who were euthyroid on admission developed sick euthyroid syndrome following treatment. ACTH, cortisol, PRL, FT3, FT4, FSH, and PRG levels are affected by acute organophosphate poisoning. The change in hormone levels may result from the effects of neurotransmitters, from the direct effect of the toxic agent, or from stress associated with events leading to the poisoning incident.