The present work reports for the first time a simple and rapid method for the spectrofluorimetric determination of lisinopril (LSP) in pharmaceutical formulations using sequential injection analysis (SIA). The method is based on reaction of LSP with o-phthalaldehyde (OPA) in the presence of 2-mercaptoethanol (borate buffer medium, pH=10.6). The emission of the derivative is monitored at 455 nm upon excitation at 346 nm. The various chemical and physical conditions that affected the reaction were studied. The calibration curve was linear in the range 0.3–10.0 mg L−1 LSP, at a sampling rate of 60 injections h−1. Consumption of OPA reagent was significantly reduced compared with conventional flow injection (FI) systems, because only 50 μL of OPA was consumed per run. The method was found to be adequately precise (sr=2% at 5 mg L−1 LSP, n=10) and the 3σ detection limit was 0.1 mg L−1. The method was successfully applied to the analysis of two pharmaceutical formulations containing LSP. The results obtained were in good agreement with those obtained by use of high-performance liquid chromatography (HPLC), because the mean relative error, er, was <1.8%.