X-ray emission from solar coronal loops changes on two different times
cales: a) flare loops and transient active region brightenings show a
rapid variability, b) quiet region loops are quasi-steady and change o
nly slowly with time. This different time behavior has been analyzed o
n the basis of Yohkoh SXT observations and we report here on the resul
ts from our analysis, mainly focussing on quiet loop variability.