A new and fast method for the determination of L-ascorbyl-2-phosphate, the 2-diphosphate, 2-triphosphate and the 2-sulfate ester in feed, fish plasma and tissue samples by capillary zone electrophoresis is described. The substances were extracted with a 200 mM potassium phosphate buffer pH 4.0. Separation was achieved using a 50 microm uncoated fused-silica bubble capillary of 40 cm length to the detector, which was set at 254 nm, and a 80 mM tricine buffer at pH 9.2. Repeatability checked on a trout feed sample revealed a migration time variation of 1.2% (n=24) and an area calculation variation of 2.8% (n=24). Detector response for L-ascorbyl-2-phosphate was linear up to at least 100 microg ml(-1). After administration of a high dose of L-ascorbyl-2-phosphate to rainbow trout, the compound was found in the stomach and intestine but not in plasma, proving a fast conversion to vitamin C.