  Measurements of the individual multiplicities of pi+, pi- and pi0 produced in
the deep-inelastic scattering of 27.5 GeV positrons on hydrogen are presented.
The average charged pion multiplicity is the same as for neutral pions, up to
approximately z= 0.7, where z is the fraction of the energy transferred in the
scattering process carried by the pion. This result (below z= 0.7) is
consistent with isospin invariance. The total energy fraction associated with
charged and neutral pions is 0.51 +/- 0.01 (stat.) +/- 0.08 (syst.) and 0.26
+/- 0.01 (stat.) +/- 0.04 (syst.), respectively. For fixed z, the measured
multiplicities depend on both the negative squared four momentum transfer Q^2
and the Bjorken variable x. The observed dependence on Q^2 agrees qualitatively
with the expected behaviour based on NLO-QCD evolution, while the dependence on
x is consistent with that of previous data after corrections have been made for
the expected Q^2-dependence.
