A homogeneous complement-mediated liposome immune lysis assay (LILA) was developed for determination of the herbicide atrazine. To dispose the antigen on the surface of lipid bilayer the atrazine was conjugated to a dimirystoylphosphatidylethanolamine (DMPE) carrier. Calcein was compared with sulforhodamine 101 as a fluorophore label for entrapping into the antigen-sensitized liposomes. The liposomes were incubated with rabbit anti-atrazine antibodies in the presence of guinea pig complement. Formation of the antigen-antibody complexes on the liposomal surface initiated the lytic action of the complement. As free competing atrazine inhibited the lytic reaction, the amount of calcein released was inversely proportional to the atrazine content in the probe. Concentration and kinetic dependences of the immunoassay were characterized to reach its maximal sensitivity. The developed assay allows detecting atrazine in concentrations up to 0.13 ng mL(-1) in the sample (0.04 ng mL(-1) in the final reaction mixture). The named sensitivity is two orders higher than those for the microplate enzyme-linked immunosorbent assay (ELISA) with the same antibodies which allows us to recommend LILA for environmental monitoring.