The toxin Ts II from the venom of the Brazilian scorpion Tityus serrulatus was purified in two successive chromatographic steps. The amino acid sequence was then determined by automated Edman degradation of the reduced and S‐carboxymethylated protein and of proteolytic peptides derived from it. This sequence appears to differ from that of previously characterized toxins found in this venom. However, it is identical to the recently published sequence of protein III‐8 from the same venom [Possani et al., J Biol Chem 266:3178–3185, 1991], except that the C‐terminus was found to be amidated. Homologies were found between the sequence of Ts II and that of other toxins from Tityus; in particular, the amino acid sequence of Ts II displays 72% sequence identity with Ts VII (also cälled TiTx γ). Consistent with this structural similarity, some biological properties of Ts II were found to be similar to those of Ts VII: Ts II has an intracerebroventricular LD50 of 6 ng, as compared to 0.6 ng for Ts VII; in a receptor binding assay Ts II, like Ts VII, was found to behave as a β‐type toxin and to inhibit the binding of the reference labelled toxin with a K0.5 of 5 × 10−9 M, as compared to 7 × 10−11 M for Ts VII. Nevertheless, Ts II is unable to bind to anti‐Ts VII antibodies in radioimmunoassay experiments, indicating the non‐conservation between the two toxins of at least some antigenically important residues. In fact, the sequence differences between Ts II and Ts VII are mainly mapped in two regions believed to be antigenic by analogy with other scorpion toxins. © 1992 Wiley‐Liss, Inc. Copyright © 1992 Wiley‐Liss, Inc., A Wiley Company