A high pressure liquid chromatographic (HPLC) method has been developed to determine lasalocid in premixes. The method is simple and rapid, requiring an extraction of the drug and separation of insoluble material before HPLC. Elution times are typically less than 10 min per sample. The average recoveries for lasalocid at the 16.5 and 50% levels were 100.2 +/- 2 and 100.0 +/- 2%, respectively. The precision of the method (coefficient of variation = 0.02) compares favorably with that of the approved bioassay (coefficient of variation = 0.06).