The rate of diffusion of indium in single crystals for two orientations has been measured using the radio‐active isotope In114. The diffusion coefficients in the directions parallel to theaaxis andcaxis are given by the Arrhenius relationsDa=34.1 exp(−25 800/RT) cm2sec−1andDc=12.2 exp(−25 600/RT) cm2sec−1, respectively. The anisotropy is discussed in terms of the vacancy mechanism of diffusion.