A sensitive and selective HPLC method was developed for the quantification of the neuromuscular blocking agent rocuronium and its putative metabolites (the 17-desacetyl derivative and the N-desallyl derivative of rocuronium) in plasma, urine, bile, tissue homogenates and stoma fluid. Samples were prepared by extraction of the biological matrix with dichloromethane, after mixing with a KI-glycine buffer. After evaporation of the organic solvent the samples were chromatographed on a reversed-phase HPLC column, using an aqueous buffer-dioxane (84:16, v/v) as the mobile phase. The aqueous buffer consisting of 0.1 M sodium dihydrogen phosphate, 0.11 mM 9,10-dimethoxyanthracene-2-sulphonate (DAS), 0.11 mM 1-heptane-sulfonic acid, was adjusted to pH 3 with orthophosphoric acid. After separation, the eluent was extracted with dichloroethane, and the organic phase was led to a fluorimetric detector, operating at 385 nm (excitation) and 452 nm (emission). The method was validated for the assay in plasma, urine, bile, tissue homogenates and stoma fluid, by determination of the repeatability, reproducibility, accuracy, lower limit of quantification, lower limit of detection, extraction recovery, effect of sample volume, and stability in the biological matrix. The method was found to be sensitive (lower limit of quantification for rocuronium in plasma is 10 ng/ml) and accurate. The interference of concomitant drugs with the assay of rocuronium and its putative metabolites has been studied extensively. In order to confirm the identity of rocuronium and its putative metabolites, a TLC method was developed. The method has been applied successfully in several pharmacokinetic studies with rocuronium.