Glycinebetaine [betaine; (Me)3-N+-CH2-COO -] is likely to contribute to osmoregulation in those plants that accumulate significant amounts of it, and hence the interest in engineering its synthesis in 'nonaccumulators'. Although only large amounts of betaine, as found in the chenopods Kochia scoparia (298.6 #mol g- 1 dry wt) and Salicornia rubra (162 #mol g-1 dry wt), would be physiologically significant, its presence in flax (Linurn usitatissirnum, 4 #mol g- 1 dry wt) and rapeseed (Brassica napus; 4.9 #mol g- 1 dry wt) indicates a genetic potential for betaine synthesis in these important plants. The liquid chromatography/continuous flow secondary ion-mass spectrometry method described here offers a 10-fold increase in sensitivity over other methods, and allows for detection of as little as 5 pmol #l- 1 of underivatized betaine. The sensitivity of this method was further demonstrated by quantitation in the range of 50-1000 pmol #1-1.