The interaction of cytotoxins Vc1, Vc5, and Vc6 of the venom of the Central Asian cobra with liposomes having a negative surface charge prepared from a mixture of phosphatidylcholine and palmitic acid (1:1, molar) has been investigated with the aid of a pyrene fluorescent probe. It has been shown that on interacting with liposomes a cytotoxin increases the microviscosity of the hydrophobic region of membranes. This effect depends on the phase state of the lipids. Observations on the kinetics of the transfer of energy between pyrene probes and diphenylhexatriene have shown that on the addition of a cytotoxin to samples of liposomes with a negative surface charge an aggregation of the liposomes takes place without a disturbance of their integrity.