A rapid and sensitive reversed phase HPLC technique was developed for the determination of seven toxic heavy metals in biological matrices. Cd, Pb, Ni, Co, Bi, Cu and Hg could be detected and quantified at ppb level in Metformin hydrochloride, a pharmaceutical product used in the treatment of certain cases of diabetes. This was achieved by the evaluation of the stability of NaDEDTC in the presence of water and different buffers at different pH-values. A direct injection/on-column derivatization HPLC procedure was developed employing NaDEDTC as chelating agent, a C-18 reversed phase analytical column and a photodiode array detector. Dilute metal ion solutions could be analyzed by direct injection of the test sample. The analysis of trace levels of metals in a pure pharmaceutical product however required the inclusion of a sample preparation step prior to analysis.