A method for the determination of lasalocid residues in animals tissues (muscles and livers) has been developed. Lasalocid was extracted from tissues with acetonitrile. The extract was washed with hexane, the hexane then was discarded and acetonitrile was evaporated under nitrogen. Residues were partitioned between water saturated during the liquid chromatography mobile phase and a mobile phase. Lasalocid was determined by liquid chromatography with a fluorescence detector (excitation at 310 m, emission at 4440 nm) and a RP C 18 column. The method permits the detection of 0.02 µg of lasalocid in 1 g of tissue, recovery being about 85%.