Changes in surface properties during expansion of the leaves of eight plant species have been examined in relation to the uptake of 1-naphthylacetic acid. Rates of wax production ranged from 0·1 ng cm-2 h-1 for sugar beet leaves to 6.2 nm cm-2 h-1 for leaves of Eucalyptus globulus. Individual leaves of all species maintained different rates of wax production at their adaxial and abaxial surfaces. Rates of synthesis of wax fractions and their constituent homologues varied with surface and leaf age. The homologue distribution shifted towards components of longer chain length as the leaves expanded. Morphological changes in wax deposits were small and limited largely to increases or decreases in the density of the plate waxes. Rates of penetration of 1-naphthylacetic acid varied between species, between leaf surfaces and with age of tissue. The highest rates of uptake were confined to the period when the leaves expanded most rapidly. The decrease in penetration rate with increase in age of the tissue, common to most plants, was greatest for grape vine and Eucalyptus globulus leaves both of which maintained high rates of wax production during expansion.