A testing methodology for evaluating the microstructural evolution of the α + β titanium alloy Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) during isothermal subtransus forging has been developed and demonstrated. A double truncated cone test geometry is isothermally deformed at subtransus temperatures to obtain microstructural information for a range of strains within a single specimen. A finite element modelling package is then employed to produce strain profiles, which correspond to the equivalent microstructural information generated from detailed backscattered SEM analysis and quantitative phase analysis. The effects of the forging temperature are also discussed to provide an understanding of the phase transformations in Ti-6246 at subtransus temperatures. © 2003 Elsevier Science Ltd. All rights reserved.