Toxins (mol. wt 32,000-35,000) were isolated from the venoms of Loxosceles gaucho, L. laeta and L. intermedia by SDS-PAGE followed by blotting to PVDF membrane. The blotted samples were sequenced in an ABI 477A/120A automatic protein sequencer. Loxosceles gaucho toxin and L. intermedia toxin showed many identical residues in their N-terminal sequence. However, L. laeta toxin showed a lower homology. A search against the NR databank at NCBI showed high levels of identity between L. gaucho (60%) and L. intermedia (75%) toxins and L. reclusa (North American brown spider) toxin. We also detected 85% of similarity between L. gaucho andL. intermedia toxins and L. reclusa toxin. Preliminary results suggested an unexpected identity (47%) and similarity (68%) between the L. laeta toxin and astacin (crayfish small-molecule proteinase). These toxins were also submitted to capillary electrophoresis peptide mapping in a 270A-HT CE System (Applied Biosystems) afterin situ partial hydrolysis of the blotted samples with 3 N HCl at 80°C for 1 week. The results obtained suggested that L. intermedia protein is more homologous with L. laeta toxin than L. gaucho toxin and revealed a smaller homology between L. intermedia and L. gaucho. Altogether, these findings suggested that toxins from Loxosceles species are probably homologous toxins. Amino acid analysis is under way for further confirmation and quantitation of this homology.