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We report here the isolation by a two-step chromatographic procedure of two new toxins from the South American scorpion Tityus bahiensis. Their amino-acid sequences and some of their biological features were established. The two toxins have different biological properties. Toxin TbIT-I had almost no activity or pharmacological effects in vertebrate tissues whereas it was lethal to house flies (LD5080.0ng/house fly). In contrast, Tb2-II was active against both mammals (intracerebroventricular injection of 100ng/mouse was lethal) and insects (LD5040.0ng/house fly). The amino-acid sequences of these toxins were established and found to be similar (60–95%) to previously described β-toxins from the Tityusgenus. Based on the available comparative information, this study attempts identify possible structure–function relationships that may be responsible for the differences in bioactivity displayed by these toxins.