  For the first time single-spin asymmetries in semi-inclusive pion production
are measured by the HERMES experiment with a transversely polarised hydrogen
target. Two different sine-modulations are extracted which can be related to
the transversity \delta q(x) and Sivers f_{1T}^{\perp q}(x) quark distribution
functions. The extracted sine-moments still contain small sub-leading twist
contributions which can be extracted from HERMES data combining the results
from the transversely polarised hydrogen target with previously measured
results from a longitudinally polarised hydrogen target.
