[en] GLOBAL acoustic oscillation modes of the Sun were discovered eleven years ago. The possibility of temporal variations in the oscillation frequencies was suggested by fluctuations in the flux of solar neutrinos, and would also be implied by changes in the solar cavity or in the speed of sound within the Sun. Our group has studied solar oscillations for many years; over the past decade, a network of three stations deployed at sites that can permit 24-h data collection has provided p-mode (acoustic) spectra of very high quality. Here we present evidence that the frequencies of the lowest-order (l ≤ 2) modes have varied over the period of observation (1977-88) in a manner that is correlated with solar activity (as measured by sunspot number). The frequency variation has a peak-to-peak amplitude of 0.46 ± 0.06 μHz, and could reflect variations in the solar dimensions or in the sound speed in the Sun, which might in turn be due to changes in solar temperature and/or magnetic field. (author)