The objective of the present study was to evaluate the effect of bicarbonate and high pH treatments separately on shoot and root growth and accumulation of organic acids in the roots of two rice cultivars differing in susceptibility to Zn deficiency. The results indicated that shoot and root dry weight of both cuitivars decreased by the treatments with bicarbonate and high pH and the decrease in shoot and root dry weight were greater when plants grown with bicarbonate than that with high pH. The inhibitory effect of bicarbonate and high pH on shoot and root dry weight of the Zn-efficient rice cultivar (S 101) was less than that of the Zn—inefficient rice cultivar (G1?2). Root length was significantly decreased by bicarbonate and high pH treatments for the Zn-inefficient n'ce cultivar ((3172); whereas was considerably enhanced by bicarbonate and high pH treatments for the Zn-efficient rice cultivar(S101), and the enhancement of root length in the Zn-efficient rice cultivar ($101) was greater when plants grown with bicarbonate than that with high pH. Both bicarbonate and high pH treatments increased the concentrations of organic acids (malic. citric, fumaric and succinic) in the roots of both cultivars, but to a greater extent for the Zn-inet'ficient than for the Zn-efficient cultivars. The results suggest that the impairment of root growth was likely to be the initial action of bicarbonate in inducing Zn-deficiency in low land rice, and the inhibitory effect of bicarbonate on root growth of the Zn-inefticient cultivar might result from high accumulation and an insufficient compartmentation of organic acids in the root cells.