A study of the potassium isotopes produced by the bombardment of argon with helium ions reveals the presence of a hitherto unknown isotope with a 22.4 hour half-life. The new potassium isotope has two beta-components of approximately 0.25-Mev and 0.8-Mev maximum energies. A gamma-component is present of roughly 0.4-Mev energy. The evidence strongly suggests that the isotope in question is ${\mathrm{K}}^{43}$ produced by the reaction ${\mathrm{A}}^{40}(\ensuremath{\alpha},p){\mathrm{K}}^{43}$.