The effect of intrathallus salt content (measured as [Na+]) on photosynthetic and dark respiratory rates in the coastal lichen Ratnalina menziesii Tayl. was investigated in three independent experiments. The first experiment demonstrated no relationship between rates of CO2 exchange in samples from a given site and distance inland, even though samples from inland sites had consistently lower salt concentrations. The second experiment showed that gas exchange rates and salt concentrations were not correlated when individual trees within one coastal and one inland site were compared. In the third experiment, thallus [Na+] was directly modified, but rates of CO2 exchange remained the same over a 27 d period. These results imply that the large variability in photosynthetic rates that is present in R. menziesii must be due to factors other than salinity.