Net fluxes of H+, K+and Ca2+ions from maize (Zea maysL.) isolated leaf segments were measured non-invasivelyusing ion-selective vibrating microelectrodes (the MIFEtechnique). Leaf segments were isolated from the bladebase, containing actively elongating cells (basal segments),and from non-growing tip regions (tip segments). Ion fluxeswere measured in response to bright white light(2600mmol m-2s-1) from either the leaf segments or theunderlying mesophyll (after stripping the epidermis).Fluxes measured from the mesophyll showed no significantdifference between basal and tip regions. In leaf segments(epidermis attached), light-induced flux kinetics of all ionsmeasured (H+, Ca2+and K+) were strikingly differentbetween the two regions. It appears that epidermal K+fluxes are required to drive leaf expansion growth, whereasin the mesophyll light-induced K+flux changes are likely toplay a charge balancing role. Light-stimulated Ca2+influxwas not directly attributable either to leaf photosyntheticperformance or to leaf expansion growth. It is concludedthat light-induced ion flux changes are associated with bothleaf growth and photosynthesis.