  We discuss the origin of the nondecoupling effects of the heavy Higgs bosons
within the two Higgs doublet extension (THDM) of the Standard Model (SM) and
illustrate it by means of the one-loop calculation of the differential
cross-sections of the process e+ e- -> W+ W- in both the decoupling and the
non-decoupling regimes. We argue that there are many regions in the THDM
parametric space in which the THDM and SM predictions differ by several
percents and such effects could, at least in principle, be testable at the
future experimental facilities.
