  We have analyzed the intermediate term periodicities in soft X-ray flare
index ($FI_{SXR}$) during solar cycles 21, 22 and 23. Power spectral analysis
of daily $FI_{SXR}$ reveals a significant period of 161 days in cycle 21 which
is absent during cycle 22 and 23. We have found that in cycle 22 periodicities
of 74 and 83 days are in operation. A 123 day periodicity has been found to be
statistically significant during the part of the current solar cycle 23. The
existence of these periodicities has been discussed in the light of earlier
results.
