The dependence of the magnetisation loops, coercivity, anisotropy constant and Delta E effect (the change of Young's modulus as a function of the magnetic field) was studied in negatively magnetostrictive Co Si-72.5 (12.5) B (15) cold-drawn amorphous wires, with a mean diameter of 100 A mu m, under annealing conditions. Samples were annealed at a temperature of 460 C-a similar to for time periods between 0.3 and 1300 min. The results indicated that progressive annealing initially led to relief of the internal stresses and that annealing of the wire at 460 C-a similar to for 90 min produced the minimum coercivity, which was similar to 0.0063 Oe. Further annealing increased the coercivity and anisotropy due to partial crystallisation at the surface. The maximum change in Young's modulus was similar to 27 % and was seen in the wire that was annealed for 60 min.