  We report on the observation of ultracold heteronuclear Feshbach molecules.
Starting with a $^{87}$Rb BEC and a cold atomic gas of $^{85}$Rb, we utilize
previously unobserved interspecies Feshbach resonances to create up to 25,000
molecules. Even though the $^{85}$Rb gas is non-degenerate we observe a large
molecular conversion efficiency due to the presence of a quantum degenerate
$^{87}$Rb gas; this represents a key feature of our system. We compare the
molecule creation at two different Feshbach resonances with different
magnetic-field widths. The two Feshbach resonances are located at
$265.44\pm0.15$ G and $372.4\pm1.3$ G. We also directly measure the small
binding energy of the molecules through resonant magnetic-field association.
