  We performed a detailed analysis of extensive photometric observations of a
sample of most active dwarf novae, that is SU UMa stars which are characterised
by supercycle lengths shorter than 120 days. We found the observational
evidence that supercycle lengths for these objects have been constantly
increasing over the past decades, which indicates that their mean mass transfer
rates have been decreasing during that time. This seems to be a common feature
for this type of stars. We present numerical results in each case and estimate
time scales of future development of these systems. This study is important in
the context of evolution of dwarf novae stars and perhaps other cataclysmic
variables.
