The chemical composition of exudate obtained from incisions made in the bark of the stem of actively growing Ricinus plants has been determined. The exudate had a high dry matter content (100-125 mg/ml), a high sugar content (80-106 mg/ml) which was solely sucrose, reducing sugars being absent. The amino acid composition was mainly glutamic and aspartic acids and threonine with a total amino acid concentration of 35.2 mM. The exudate had a pH of 8.0-8.2. Potassium was the major cation (60-112 mM) with sodium present at a lower concentration (2-12 mM). Of the divalent cations, calcium was at a low concentration (0.5-2.3 mM) and magnesium relatively higher (4.5-5.4 mM). Chloride was the major inorganic anion (10-19 mM). Phosphate concentration was relatively high (3.7-5.7 mM) and low concentrations of sulphate (0.3-0.5 mM) and bicarbonate (1.7 mM) were also present. Nitrate was absent. The ionic balance was maintained by the presence of relatively large quantities (30-47 meq/l) of organic anions, mainly malate. Bioassays revealed auxin, gibberellin and cytokinin activities in chromatographed exudate. Adenosine triphosphate was found in the exudate (0.40-0.60 mM). The analysis is dicussed with respect to the composition of phloem sap reported for other plant species.