Carbon dioxide resistance and water content curves are presented for Pseudocyphellaria amphisticta, P. homoeophylla, P. billardierii, P. colensoi, Sticta latifrons and Peltigera dolichorhiza. In all cases the curves are triphasic with a high resistance at low and high water contents and a low resistance at intermediate water contents. The exact water contents at which these changes in resistance occur, and the rate at which the resistance increases at the higher water contents, appear to be species specific. The depressed NAR often found at higher water contents is shown to be caused in part by the increased resistance since it occurs under conditions where there are no changes in respiratory rate. The increase in resistance at higher water contents is suggested to be a result of water on the lower cortex.