New limits are reported on right-handed currents, based on precise measurement of the $e^{+}$ spectrum end point in ${\mu }^{+}$ decay. Highly polarized muons from the TRIUMF "surface" beam were stopped in metal foils within a 1.1-T spin-holding longitudinal field or a 70-G spin-precessing transverse field. For the spin-held data, the $V-A$ decay rate vanishes in the beam direction at the end point. Measurement of this rate sets the 90%-confidence limits $\frac{\xi P_{\mu }\delta }{\rho }>0.9959\mathrm{}$ and $M\left(W_R\right)>\mathrm{}380\mathrm{}$ GeV, where $W_R$ is the possible righthanded gauge boson.

• Received 8 June 1983

DOI:https://doi.org/10.1103/PhysRevLett.51.627