Morphological and physiological characteristics of micropropagated plants of Delphinium cv. Princess Caroline were studied. Leaves produced in vitro showed poor control of water loss which appears to result from restricted responses by stomata and not from poor cuticular development. Stomata of leaves produced in vitro were larger and more frequent than those produced during acclimatization. Despite the fact that stomata from isolated epidermis of leaves produced in vitro reduced their apertures when exposed to turgor-reducing treatments, they did not close fully. This, together with high stomatal frequencies might explain the poor control of water loss shown by intact leaves produced in culture when exposed to dry air. While leaves from acclimatized plants showed almost complete closure with ABA, low water potentials, darkness and CO2, stomata from leaves produced in vitro reduced their apertures when exposed to those factors, but only to a limit. Therefore, stomata from leaves cultured in vitro seem to be partially functional, but some physiological or anatomical alteration prevents them from closing fully. Stomata from leaves produced in vitro were particularly insensitive to ABA which appears to be partly associated with the high cytokinin concentration in the culture medium. In the long-term, this stomatal insensitivity to ABA might contribute to plant losses when micropropagated plantlets are transferred to soil.