  We prove the Bisognano-Wichmann property for asymptotically complete
Haag-Kastler theories of massless particles. These particles should either be
scalar or appear as a direct sum of two opposite integer helicities, thus,
e.g., photons are covered. The argument relies on a modularity condition
formulated recently by one of us (VM) and on the Buchholz' scattering theory of
massless particles.
