Thermal conductivities of fresh leaves, both unmodified and infiltrated with water, were measured. Samples were placed between silver plates of known and differing temperatures, and the time required to boil off a constant volume of liquid was measured. The species used are evergreens: Eucalyptus globulus Labill. (sclerophyllous) with isolateral leaf symmetry; and Peperomia obtusifolia A. Dietr. (succulent), Citrus limon Burm. f. (mesophyllous), Arbutus menziessii Pursh. (sclerophyllous), and Heteromeles arbutifolia M. Roem. (sclerophyllous), all with bilateral leaf symmetry. Mean values found were in the range of 0.268 to 0.573 W/m · °C for fresh leaves, and 0.540 to 0.548 W/m · °C for leaves infiltrated with water. An analysis of errors in the technique indicated that these values may be somewhat low. These results are several times higher than previously reported values. It is concluded that ordinary mesophytic and xerophytic leaves will not develop large gradients in temperature between the surfaces.