The objective of the present study was to assess whether, in barley, nitrogen supply limits the rate of leaf elongation through a reduction in (relative) cell elongation rate and whether this is attributable to a reduced turgor, a reduced availability of osmolytes or, by implication, changed wall properties. Plants were grown on full-strength Hoagland solution (``Hoagland''-plants), or on N-de®cient Hoagland solution while receiving N at a relative addition rate of 16 or 8% N á plant-N A1 á d A1 (``16%-'' and``8%-plants''). Hoagland-plants were demand-limited, whereas 16%-and 8%-plants were supply-limited in N. Third leaves were analysed for leaf elongation rate and ®nal epidermal cell length, and, within the basal growing region, for the spatial distribution of relative segmental elongation rates (RSER, pin-pricking method), epidermal cell turgor (cell-pressure probe), osmotic pressure (OP, picolitre osmometry) and water potential (Y). During the development of the third leaf, plants grew at relative growth rates (relative increase in fresh weight ) of 18.2, 15.6 and 8.1% á d A1 (Hoagland-, 16%-and 8%-plants, respectively). Final leaf length and leaf elongation rate were highest in Hoagland plants (ca. 34.1 cm and 2.33± 2.60 mm á h A1 , respectively), intermediate in 16%-plants (31.0 cm and 1.89±1.96 mm á h A1 ) and lowest in 8%-plants (29.4 cm and 1.41±1.58 mm á h A1 ). These dierences were accompanied by only small dierences in ®nal cell length, but large dierences in cell-¯ux rates (146, 187 and 201 cells á cell-®le A1 á d A1 in 8%-, 16%-and Hoagland-plants, respectively). The length of the growth zone (32±38 mm) was not much aected by Nlevels (and nutrient technique). A decrease in RSER in the growth zone distal to 10 mm produced the signi®-cant eect of N-levels on leaf elongation rate. In all treatments, cell turgor was almost constant throughout the growing region, as were cell OP and Y in 16%-and 8%-plants. In Hoagland-plants, however, cell OP increased by ca. 0.1 MPa within the zone of highest elongation rates and, as a consequence, cell Y decreased simultaneously by 0.1 MPa. Cell Y increased considerably where elongation ceased. Within the zone where dierences in RSERs were highest between treatments (10±34 mm from base) average turgor was lowest, OP highest and Y most negative in Hoagland-compared to 8%-and 16%-plants (P < 0.001), but not signi®cantly dierent between 8%-and 16%-plants.Abbreviations and symbols: LER = leaf elongation rate; OP = osmotic pressure; Y = water potential; RAR = relative addition rate; RIFW = relative increase in fresh weight; RSER = relative segmental elongation rate