  We evaluate the fluxes of neutrinos and muons from charmed particles produced
by cosmic ray interactions with air nuclei. Using next-to-leading order
perturbative QCD, we compare our results with calculations based on a PYTHIA
Monte Carlo evaluation of charm production. We investigate the sensitivity of
our results to the choice of parton distribution functions and the cosmic ray
spectrum. Perturbative QCD yields larger lepton fluxes than the PYTHIA
evaluation. The flux of muons from charm dominates the muon flux from pion and
kaon decays for energies above $\sim 10^5$ GeV.
