  We present a search for the decays B+ -> mu+ nu_mu and B+ -> e+ nu_e in a 253
fb-1 data sample collected at the \Upsilon(4S) resonance with the Belle
detector at the KEKB asymmetric-energy B factory. We find no significant
evidence for a signal and set 90% confidence level upper limits of B(B+ -> mu+
nu_mu) < 1.7 x 10^{-6} and B(B+ -> e+ nu_e) < 9.8 x 10^{-7}.
