Measurements of the turbulent fluctuations of wind, temperature and humidity were made in the atmospheric surface layer. The statistics of the fluctuations were investigated in both the time and frequency domains. The vertical wind, temperature and smaller-scale horizontal wind fluctuations appear to obey the Monin-Obukhov similarity hypothesis. The humidity fluctuations were found to be governed by a humidity flux stability parameter rather than the normal Monin-Obukhov length.