We consider the classical linear theory of electromagnetic wave growth in a warm plasma for waves propagating parallel to a uniform ambient magnetic field. Wave growth rates &ggr; are calculated for ion-driven right-hand mode waves for Kappa (bi-Lorentizian) and Maxwellian particle distribution functions. Systematic calculations of &ggr; are carried out for various values of the spectral index &kgr;, the temperature anisotropy A+=1-(T+⊥/T+∥), and the ratio &bgr;+ of plasma pressure to magnetic pressure, appropriate to the solar wind. When the anisotropy is low (A+≪1), the wave growth is limited to frequencies below the proton gyrofrequency, and growth rate increases dramatically as the spectral index &kgr; is reduced (i.e., as the high-energy tail becomes more pronounced). The growth rate for any Kappa distribution greatly exceeds (often by several orders of magnitude) that for a Maxwellian with the same bulk properties. For large thermal anisotropy (T+∥≫T+⊥) the growth rate from either distribution is greatly enhanced. In comparison to a maxwellian distribution the growth rates from a Kappa distribution are generally larger, and significant wave growth occurs over a broader range of frequencies. Evidently, the theory is important in the study of microinstabilities in space plasmas in which a high-energy tail distribution is generally present. ¿American Geophysical Union 1991