The first observation of Pontecorvo reactions of the type pdBAR --> Xn
is reported. The outgoing meson is fully reconstructed, and the follo
wing preliminary branching ratios are found for antiprotons stopped in
liquid deuterium: BR(pdBAR --> pi0n) = (7.31 +/- 0.64) x 10(-6), BR(p
dBAR --> etan) = (2.91 +/- 0.44) x 10(-6), BR(pdBAR --> omegan) = (22.
6 +/- 5.5) x 10(-6), BR(pdBAR --> eta'n) = (13.5 +/- 4.3) x 10(-6).