Following many years of few earthquakes, the seismicity of Mauna Loa increased markedly in 1974. Well determined foci of 171 earthquakes with magnitudes between 1.5 and 4.6 in 1974, as well as the locations of other earthquakes from 1962 to 1973, outline a broad seismic zone around the summit. Most earthquakes are at depths less than 15, km; some are as deep as 50 km. The significant increase in seismicity, combined with expansion measured as the summit, suggest that Mauna Loa may be reawakening after nearly 25 years of quiescence.