The technique of photon-correlation spectroscopy (intensity fluctuation spectroscopy) is applied to light scatter from type 5 adenovirus undergoing Brownian motion in solution and the translation diffusion coefficient (D20,w) measured to be 0,367 +/- 0.003 Fick units. Using Svedberg's equation with previously determined parameters, a molecular weight of 165 - 10(6) +/- 5 - 10(6) is obtained.