The 32-Hz electric field data measured by the electric field detector EFD-P on board the EXOS D satellite show pulse-like distortions (PLDs) in nearly 10% of 1000 paths selected at random from April 1989 to June 1990. The purpose of the present paper is to analyze these distortions as a basis for future measurements of the parallel electric field in space. The PLDs are observed at altitudes higher than about 3000 km, with a typical duration of a few tens of minutes. Comparing with data obtained by other detectors on board EXOS D, it is suggested that the necessary conditions for the appearance of the distortions are (1) low plasma density, which implies a large Debye sphere around the spacecraft, (2) low ambient electron flux, which is necessary to keep the spacecraft potential high enough to attract photoelectrons from the probes, (3) small angle between the magnetic field and the wire probe, which makes the photoelectrons emitted from the probe accessible to the satellite, and (4) asymmetry in the photoelectron current from a pair of probes. When all four of these conditions are satisfied simultaneously, then the photoelectrons emitted from the probes reach the spacecraft body and produce spurious current flows in the measurement circuit to generate PLDs. A generation mechanism proposed here can explain well all the observed properties of PLDs. ¿ 1998 American Geophysical Union