  COMPASS final results on multiplicities of charged hadrons and of identified
pions and kaons produced in the deep inelastic muon scattering off an isoscalar
target are presented and compared to HERMES results. Measurements are done in
bins of x, y and z in a wide kinematic range. The hadron and pion data show a
good agreement with (N)LO QCD expectations. The kaon data are long awaited for
since they are needed to extract kaon fragmentation functions, a crucial
ingredient in solving the strange quark polarisation puzzle. COMPASS results
for kaons differ from the expectations of the old NLO DSS fit and they cannot
be well described by LO QCD either. In this context the importance of
$K^-$/$K^+$ multiplicity ratio at high z is discussed.
