The transport properties of glucosinolates within Brassica napus are of interest as identification of the mechanism of transport could lead to lower levels being obtained in specific tissues such as the seeds. The phloem mobility of 35S-gluconapin (but-3-enylglucosinolate) and 35S-desulphogluconapin in oilseed rape plants has been inferred from tissue distribution patterns, as well as from observed coincident phloem mobility of 3H-gluconapin and 14C-sucrose. The measured relative phloem mobilities for sinigrin (2-propenylglucosinolate), 3H-gluconapin, 35S-desul-phogluconapin, 35S-desulphosinigrin, 14C-tryptophan, 3H-AIB (α-aminoisobutyric acid), and literature values for a reduced 3H-oligogalacturonide elicitor (degree of polymerization 6) and 14C-IAA (indolylacetic acid), have been compared with the predicted values obtained using the Kleier model for phloem mobility of xenobiotics. All the above compounds show phloem systemicity, demonstrated using the Ricinus assay, as predicted by the model. Log Kow (octanol-water partition coefficient) values for glucosinolates and desulphoglucosinolates measured at pH 4 and pH 7, and the effect of pH on uptake by oilseed rape embryos are provided as evidence against a weak acid trap mechanism acting in either the phloem mobility or the accumulation of glucosinolates in oilseed rape embryos. The phloem mobility of glucosinolates is explained by the intermediate permeability hypothesis. In conclusion, it would appear that glucosinolates like other groups of endogenous compounds have physicochemical properties allowing phloem mobility as predicted by the Kleier model.