1. We describe a "sandwich" enzyme-linked immunosorbent assay (ELISA) sensitive to quantities of scorpion (Tityus serrulatus) venom (TsV) in the range of 1-3 ng/ml sample. 2. Cross-reactivity with the venom from the rattlesnake Crotalus durissus terrificus and with venoms from several snakes of the Bothrops genus was detected only at concentrations higher than 1 microgram/ml sample. 3. A conventional ELISA is also described for the detection of antibodies against TsV. 4. Analysis by Western Blot (WB) demonstrated a 25-kDa protein band common to TsV and to the venoms of Bothrops moojeni, B. jararacussu and B. jararaca. 5. Venom from C. d. terrificus exhibited WB cross-reactive bands of 16 and 25 kDa with TsV.