Immunogens for preparing antibodies against the drug lidocaine and related compounds, labeled conjugates, synthetic intermediates, and the use of such antibodies and labeled conjugates in immunoassays for determining lidocaine and such related compounds. The immunogens comprise lidocaine or an analog thereof coupled through one of the aromatic methyl groups to a conventional immunogenic carrier. The antibodies and labeled conjugates are particularly useful in homogeneous nonradioisotopic immunoassays for measuring lidocaine or its analogs in biological fluids such as serum.