The motion of LDV seeding particles under the influence of viscous and thermophoretic forces in the rapidly-accelerating, high-temperature-gradient flame environment was studied via the counterfiow premixed twin-flame configuration. Results demonstrate that thermophoretic force can induce significant lag between the fluid and,particle velocities in the active preheat zone of a flame, and suggest that caution should be exercised when interpreting LDV data obtained in this region. A thermophoretic velocity correction to the LDV-determined velocity, with known experimental or computational temperature profile, is proposed. Additional considerations of LDV diagnoslics and its determination of laminar flame speed are also presented.