The high temperature steady state deformation behaviour of PbSn eutectic alloy was investigated over wide ranges of grain size (9.7 - 32.0 μm), temperature (298 - 443 K) and strain rate (10-7 - 10-2 s-1), after stability of microstructure and strength had been achieved through prior tensile deformation. The σ-ε{lunate} plots for these materials consisted of regions II and III. In region II the strain rate sensitivity index m is 0.6 ± 0.1 and the grain size exponent p is 3.34 ± 0.23. The activation energy Q in region II was found to depend on temperature with Q = 44.7 ± 1.1 kJ mol-1 below about 408 K and Q = 81.1 ± 3.9 kJ mol-1 above this temperature. These experimental parameters do not agree with any of the superplasticity models that have been proposed to date. However, in region III the parameters m = 0.09 ± 0.01, p = 1.00 ± 0.72 and Q = 100.0 ± 8.8 kJ mol-1 observed are in better agreement with the recovery creep model of Gifkins. © 1981.