[en] Experiments searching for parity nonconservation in the scattering of 1.5 GeV/c (800 MeV) polarized protons from an unpolarized water target and a liquid hydrogen target are described. The intensity of the incident proton beam was measured upstream and downstream of the target by a pair of ionization detectors. The beam helicity was reversed at a 30-Hz rate. Auxiliary detectors monitored beam properties that could give rise to false effects. The result for the longitudinal asymmetry from the water is A/sub L/ = (1.7 +- 3.3 +- 1.4) x 10^-7, where the first error is statistical and the second is an estimate of systematic effects. The hydrogen data yield a preliminary result of A/sub L/ = (1.0 +- 1.6) x 10^-7. The systematic errors for p-p are expected to be < 1 x 10^-7