DESY-HERA. Measurement of the longitudinal spin asymmetry in photoproduction of pairs of oppositely charged hadrons with high transverse momentum. Data arecollected using a 27.5 GeV polarized positron beam and a polarized hydrogen int eral to the HERA storage ring.. The longitudinal cross section asymmetry ASYM(NAME=A-PARALLEL) is defined as (N+-L++ - N++L+-)/(N+-L(P)++ + N++L(P)+-), where N++(+-) are the numbers of oppositely charged hadron pairs for target spin parallel (anti-parallel) to the beam spin orientation. L++(+-) are luminosities for the different spin orientations and L(P)++(+-) are the same but weighted by the product of the beam and target polarization values for each spin state.