Conventional planar magnetrons have been characterized with small (0.01 and 0.02 cm diam) Langmuir probes in the plasma region and also extending into the sheath. The plasma potentials, electron temperatures, and electron densities have been measured at low and intermediate magnetron discharge currents. The low currents reduce the effect of the probe on the discharge by reducing probe heating. The pressure range examined was 1.5-30 mTorr in both Ar and He. With Ar, the plasma potential is relatively constant in the abnormal (bright) glow region of the magnetron, and only begins to drop appreciably in the dark space (< 1 mm thick) near the cathode. The electron temperatures showed a continual increase as the cathode sheath was approached. Temperatures were measured in the 1–5 eV range at 5–30 mTorr Ar, and as high as 22 eV at pressures of 1.5 mTorr Ar. The measured electron densities were also pressure dependent and were highly peaked in the bright glow region near the cathode surface. The densities fell rapidly through the sheath. Significant departures from a Maxwellian electron energy distribution were found for the He plasmas, with a higher proportion of electrons in the high energy tail. The densities, however, were significantly lower than with Ar. © 1986, American Vacuum Society. All rights reserved.