Lytic peptides such as melittin and mastoparan are usually assayed by measuring the leakage of cell contents; e.g., hemolysis. When such peptides lyse liposomes containing concentration-quenched 6-carboxyfluorescein (6CF), the resulting fluorescence increase is proportional to the amount of lytic peptide added. Using this 6CF-liposome system, one can assay nanogram quantities of melittin. A protocol was developed to survey peptides for lytic activity and at the same time, to test for mast cell degranulating activity. Peptides possessed either, both, or neither of these activities. The dye-liposome system was used to assay HPLC fractions of bee venom. This fluorescence assay for lytic activity is more sensitive and convenient than the hemolysis method, does not require removal of unlysed structures, and does not require animal cells.