In experiments on particle-antiparticle production by electron positron colliding beams, cosmic rays give a considerable contribution to total background. In particular, a large fraction of the cosmic rays which pass through the interaction region cannot be distinguished from events produced by interaction between the two beams, even when spark chamber pictures are used. A time-of-flight measurement between two counters of the experimental set up, separated by a distance d as shown in fig. 1, allows us to distinguish cosmic rays from pairs of charged particles produced by an annihilation event. This time-of-flight is of the order of some ns(≈4÷8 ns, 1 ⪅ d⪅2 m) when a cosmic ray passes through the two counters, whereas it is zero for two charged particles produced in the interaction region. When large scintillation counters are used, the main difficulty in measuring and distinguishing these time intervals arises from the finite transit time of light in scintillators. By properly applying double time-of-flight methods 1–3) it is possible to minimize these effects. In this paper we show results of time-of-flight measurements between two 100 × 100 × 2 cm 3 scintillation counters. A time resolution of ±0.7 ns has been obtained. A method to distinguish direction (right ⇄ left, up ⇄ down) of cosmic rays is proposed.