Seventeen patients stung by Tityus serrulatus scorpion were classified as mild (pain at the site of the sting, n = 6), moderate (local pain and one of the following manifestations: vomiting, psychomotor agitation, prostration, sweating, tachypnea, tachycardia and mild arterial hypertension, n = 10) and severe cases (equal moderate cases plus cardiac failure, pulmonary edema and shock, n = 1). Venous blood was sampled for biochemical and hematological analysis and for IL-1alpha, IL-6, IL-10, TNF-alpha, IFN-gamma and GM-CSF ELISAs at the time of hospital admission, 6 h (moderate and severe cases), and 12, 18, 36 and 72 h (severe case) later. Ten age-matched healthy volunteers were used as control. Increased serum levels of IL-1alpha was noticed in all patients, high levels of IL-6, IFN-gamma and GM-CSF were observed only in a patient with severe envenomation. Our data suggest that a systemic inflammatory response-like syndrome is triggered during severe envenomation caused by T. serrulatus sting and that release of cytokines may be involved in this response.