  We comment on theoretical aspects of the measurement of azimuthal asymmetries
in semi-inclusive charged particle production, made recently by the ZEUS
Collaboration at HERA. By taking the ratio of the two measured asymmetries, we
find good agreement between the perturbative QCD prediction and the
experimental data. To separate the perturbative and nonperturbative
contributions to the asymmetries, we suggest that the azimuthal asymmetries of
the transverse energy flow be measured as a function of a variable $q_T$
related to the pseudorapidity of the energy flow.
