Electric and magnetic field changes associated with lightning return strokes have been observed by waveform recording systems and a magnetic direction-finding system on the coast of the Sea of Japan. Parameters characterizing the fine structure of a return-stroke field waveform are statistically investigated. The 10-bit resolution of the recording system revealed long duration of the slow front, resulting in the 0--100% risetime of 8.6 μs mean for negative and 13.2 μs for positive return strokes in summer. The values are about 1.5--2 times those previously reported. The risetime for positive return-stroke waveforms shows seasonal variation, and the mean in winter is 21.2 μs, which is consistent with the previous report of the authors. Fast transition in the wave front was measured with a fast antenna of 24-ns overall risetime. The 10--90% risetime of the fast transition for positive return-stroke waveforms propagated over seawater shows a similar distribution to that for negative return strokes obtained in Florida. The mean and standard deviation are 0.11 μs and 62 ns, respectively. The zero-crossing time for radiation waveforms from return strokes shows seasonal variation in both polarities and becomes shorter in winter. Dependence on polarity also exists. The mean values for negative return strokes are 79 and 40 μs in summer and winter, and those for positive return strokes are 151 and 93 μs, respectively. The zero-crossing time for negative return strokes in summer is about 1.5 times longer than the value measured in North America, but the difference might come from the characteristics of the measuring device, as is the case for the 0--100% risetime. The depth of the dip after the peak of return-stroke waveforms also has seasonal variation and dependence on the polarity of return strokes. The mean of 42% for negative return strokes in summer increases to 78% in winter and, similarly, increases from 24% to 40% for positive return strokes. ¿ American Geophysical Union 1989