The apical 12 mm of roots of intact 2 day old maize plants were immersed for 1h in buffer with or without ABA (10-6M), labelled radioactively or not. The techniques of GC-MS and liquid scintillation counting were used to determine endogenous ABA and the amount of ABA taken up. This combination of a radio-tracer study and GC-MS analyses enabled us to calculate the amount of ABA taken up and remaining as ABA at the end of the experiment and the amount of ABA which had been metabolised. Hence the turnover of the labelled ABA was calculated. The uptake of applied ABA over 1 h was 8 times the level of the endogenous hormone in the 1-5 mm elongation zone of the root, and 4 times the endogenous level in the 5-12 mm differentiation zone. This difference in uptake between the zones may be attributable to various factors such as the presence of a carrier for ABA uptake in the apical part of the maize root. Over 1 h the turnover of the ABA which had been taken up was about 160 % for the apical zone and about 75 % for the differentiation zone.