  We present the principles of the measurement of the quark transversity
distributions in semi-inclusive deep inelastic electron scattering, which form
the basis of HELP and one of the ELFE proposals. A string model for
Collins-type asymmetry in polarized quark fragmentation function is proposed. A
possible role of the Collins effect in the single spin asymmetries observed by
experiment E 704 at Fermilab is suggested.
