An investigation of the relationships between New South Wales (NSW) seasonal rainfalls and fluctuations of geopotential height at four Australian radiosonde stations is presented. The connection between the Southern Oscillation Index (SOI) and the geopotential height was explored up to the mid-troposphere. The study determined that the 800 and 600 hPa heights at Woomera show stronger and more consistent correlations with winter and spring rainfalls respectively, than occur between SOI and rainfall. The 900 hPa height at Brisbane is also strongly correlated with autumn rainfall for much of coastal NSW. These correlations are found to be stable during high and low phases of the SO cycle. It was found that the effects of the considered geopotential data on rainfall are independent of the influence of the SO phenomenon. The study also found that the fluctuations of geopotential heights at Woomera are related to rainfall variability over a wide region of southern Australia. At Darwin the 800 hPa surface appears to be the highest altitude at which there is any influence from the Southern Oscillation during winter. Furthermore, airmass movement over inland NSW is quite strongly related to SOI but coastal airmass movement is only weakly related to SOI. A mechanism for the influence of the Southern Oscillation on NSW rainfall is suggested.