SLAC. Measurement of the asymmetry, ASYM(NAME=A-PARALLEL), for inclusive hadron production on longitudinally polarized proton and deuteron targets by circularly polaraized photons. The photons are produced via internal and external bremsstrahlung from a 48.35 GeV electron beam. The asymmetry measurments are made for both positive and negative hadrons, and a subset of identified pions, in the momentum range 10 to 30 GeV at two angles.. The helicity-dependent asymmetry is defined by: (N(-)-N(+))/(N(- )+N(+))/(f& apos; Pb Pt ), N(-) (N(+)) is number of detected hadrons per incident charge for negative (negative) beam helicity, and f& apos; is the dilution factor representing the fraction of measured events originating from polarizable protons or deuterons within the target.