A novel, simple technique using reversed phase thin-layer chromatography has been developed to separate beta-endorphin, beta-lipotropin and Met- and Leu-enkephalins. This method is useful for the rapid determination of the purity of these opioid peptides. The effectiveness of several solvent systems has been assessed. The resolution between beta-endorphin and beta-lipotropin achieved by this method exceeds that reported using high performance liquid chromatography or a variety of column techniques. This system also eliminates the problem of unrecognized loss of peptide due to binding on HPLC or other types of columns since the entire stationary phase is visualized using fluorescamine detection. Efficient, inexpensive and reliable simultaneous separation with visualization of several opioid peptides, their peptide precursors and their degradation products is now possible using the new technique. Such separations are required for many purposes including preparation of samples for radioimmunoassay of opioid peptides.