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An experiment (E497) is underway at TRIUMF to measure the angleintegrated, parity violating longitudinal analyzing power, A z , in proton-proton elastic scattering, to a precision of ±0.2 × 10 −7 . The experiment uses a 221 MeV longitudinally polarized proton beam incident on a 40 cm liquid hydrogen target. The beam energy is carefully chosen so that the contribution to A z from the J=0 parity mixed partial wave ( 1 S 0 − 3 P 0 ) integrates to zero over the acceptance of the apparatus, leaving the experiment sensitive mainly (> 95%) to A z arising from the 3 P 2 − 1 D 2 , J=2 wave. To minimize sources of systematic error, the TRIUMF ion source and cyclotron parameters have been refined to the extent that helicity correlated beam changes are at an extremely low level, and specialized instrumentation on the E497 beamline is able to measure residual helicity correlated modulations to a precision consistent with the goals of the experiment. A data taking run in February-March, 1997 logged approximately 12% of the desired data and produced a preliminary result, A z = (1.1 ± 0.4 ± 0.4) × 10 −7 , where the error is statistical only.