  We search for decays of a B meson into a neutral D meson and a kaon, with the
D meson decaying into K+pi-pi0. This final state can be reached through the b
--> c transition B- -> D0K- followed by the doubly Cabibbo-suppressed D0 -->
K+pi-pi0, or the b --> u transition B- --> D0bar K- followed by the
Cabibbo-favored D0bar --> K+ pi-pi0. The interference of these two amplitudes
is sensitive to the angle gamma of the unitarity triangle. We present
preliminary results based on 226 10^{6} e+e- --> Y(4s) --> BBbar events
collected with the BABAR detector at SLAC. We find no significant evidence for
these decays and we set a limit R_ADS =(BR(B- -->[K+pi-pi0]_D K-)+ BR(B- -->
[K-pi+pi0]_D K+))/(BR(B- -->[K-pi+pi0]_D K-)+ BR(B- --> [K+pi-pi0]_D K+))<0.039
at 95% confidence level, which we translate with a Bayesian approach into r_B =
|A(B- --> D0bar K-)|/|A(B- --> D0bar K-)| < 0.185 at 95% confidence level.
