We report the first detection of interstellar nitrogen sulfide (NS) in cold dark clouds. Several components of the (2)Pi1/2, J = 3/2 to 1/2 and J = 5/2 to 3/2 transitions were observed in TMC-1 and L134N. The inferred column density for TMC-1 is NNS approximately 8 x 1012/sq cm toward the NH3 peak in that cloud, and in L134N is NNS approximately 3 x 1012/sq cm toward the position of peak NH3 emission. These values correspond to fractional abundances relative to molecular hydrogen of fNS approximately 8 x 10-10 for TMC-1, and fNS approximately 6 x 10-10 for L134N. The NS emission is extended along the TMC-1 ridge and is also extended in L134N. The measured abundances are significantly higher than those predicted by some recent gas phase ion-molecule models.