The Southern Oscillation Index (SOI), its relationship with precipitation, and how greenhouse gas-induced changes in climate may modify these relationships has been examined in 12 coupled atmosphere-ocean Global Climate Model (GCM) experiments. The model SOI series predominantly show a tendency towards more positive (La Niña-like) SOI values as climate warms, but opposing trends with regard to changes in its interannual variability. EOF analyses of the dominant mode of precipitation reveals that most models display the main observed features of tropical precipitation related to ENSO. Only modest changes in the modelled EOF1 coefficient fields between the simulated periods 1900–1949 and 2050–2099 are found. The model EOF1 amplitude series, in general, correlate highly with the model SOI series for the historic 1900–1949 period. For the future 2050–2099 period, however, this correlation decreases in a number of the simulations, due either to a shift in the centres of ENSO action or to an overall weaker SOI signal.