  We report the calculation of the interspecies scattering length for the
sodium-rubidium (Na-Rb) system. We present improved hybrid potentials for the
singlet $X^1\Sigma^+$ and triplet $a^3\Sigma^+$ ground states of the NaRb
molecule, and calculate the singlet and triplet scattering lengths $a_{s}$ and
$a_{t}$ for the isotopomers $^{23}$Na$^{87}$Rb and $^{23}$Na$^{85}$Rb. Using
these values, we assess the prospects for producing a stable two-species
Bose-Einstein condensate in the Na-Rb system.
