The transition to region II at ~ ~< 10-4 sec -1 is consistent with several sets of data showing that the strain rate sensitivity increases at a testing temperature of 298 K when the strain rate is reduced below about 10-4 sec -1 [10, 12-14, 17]. However, the measurements presented earlier [18] of the elongations to fracture were conducted with a grain size of 6.1pro, and detailed experiments on the superplastic Zn-22 wt % A1 eutectoid have shown that a reduction in grain size leads to the occurrence of region II at faster strain rates and thus to higher ductilities at the faster rates of strain [19]. Accordingly, the present experiments were conducted to investigate the elongations to failure of the Pb-Sn eutectic having the smallest grain size available after the fabrication procedure. The alloy was produced from 99.999% purity lead and 99.995% purity tin by melting in air in a graphite crucible, chill-casting into an ingot with a thickness of 1.0 cm, and rolling at room temperature to a sheet thickness of 0.254cm. The final material contained 38 wt % Pb, 62 wt % Sn, and the following minor impurities in ppm: Ag 0.2, A1 0.5, Au 1, Bi 0.7, Ca 0.1, Cd 0.1, Cu 2, Fe 1, In 1, Mg 0.2, Mn 0.1, Si 0.3 and T1 0.5. The average spatial grain size after fabrication, and without any pre-test annealing treatment, was d = 1.74 x E = 3.3 pm, where /~ is the value of the mean linear intercept. The accuracy of these, and subsequent grain size measurements, was estimated as + 10%. Tensile specimens were cut parallel to the rolling direction with a gauge length of 1.27 cm and a gauge width of 0.64 cm. Each specimen was tested at room temperature (298-+ 2K), without a prior annealing treatment, by pulling to failure in an Instron machine operating at a constant rate of crosshead displacement: the equivalent initial strain rates were in the range from 6.6 x 10 -s to