Changes induced by blue light (BL) in ion fluxes and pH in etiolated seedlings of dicotyledons ( Cucumis sativus L., Phaseolus lunatus L., Pisum sativum L.) were studied using a non-invasive ion-selective microelectrode technique (MIFE). BL induced significant Ca2+ uptake within the first 5 min after onset in upper parts of the whole cucumber seedling. To locate the sites of the BL perception, studies on excised segments were performed. The data obtained demonstrated that the observed Ca2+ uptake is associated with the very top of the hypocotyl hook of cucumber and butter bean, and with the whole epicotyl of pea, although the response was stronger for the upper parts of the epicotyl. Addition of Gd3+ and La3+ into the bathing solution completely prevented Ca2+ influx, implicating the involvement of Ca2+ channels in the regulation of Ca2+ transport during BL exposure. BL-induced changes in H+ and Ca2+ fluxes were not likely to be linked to the one mechanism, as they were separated spatially and pharmacologically.