P-odd observables at the Upsilon peak

We study the gamma-Z interference In the process e(+)e(-) -> Y --> tau(+)ta u(-) as a means to measure the neutral current coupling of the b-quark. The helicity amplitudes are calculated from resonant and background diagrams a nd the spin density matrix of the final state is discussed. The spin analyz er of the tau's is illustrated with the decays pi nu and rho nu --> (pi pi) nu. With 10(8)Y a sensitivity to g(V)(b) of a few per cent could be reachab le.