Plasma-density structures related to a night-time sporadic-E layer were measured by a fixed-bias Langmuir probe during the flight of the S310-25 sounding rocket, launched at 2300:00 JST on August 26, 1996 as part of the SEEK campaign. Large plasma-density fluctuations were observed during the upleg of the rocket trajectory at altitudes of 90 to 130 km. Intense electron-density irregularities with kilometer scales were found to be well correlated with strong polarization dc electric fields measured simultaneously by double probes. Meter-scale irregularities measured with the Langmuir probe were found to exist in a similar altitude range as the quasi-periodic (QP) echoes detected with a frequency agile radar operated at 24.5 MHz. However, the detailed altitude structures differed from one another. The preliminary results suggest that the regions probed by rocket and radar contained different spatial structures. ¿ 1998 American Geophysical Union