  Search for \beta \beta -decay of Xe-136 with two high pressure proportional
counters is carried out in Baksan Neutrino Observatory. The experiment is based
on comparision of spectra measured with natural and enriched xenon. The
measured halfe life is equal to T_{1/2}=5.5^{+4.6}_{-1.7} \cdot 10^{21} yr (67%
C.L.) for \beta \beta 2\nu -decay mode. No evidence has been found for
neutrinoless \beta \beta -decay. The decay half life limit based on data
measured during 17280 h is T_{1/2}(\beta\beta 0\nu)\geq 4.9 \cdot 10^{23} yr
(90% C.L.).
