A radioimmunoassay (RIA) for a human lung tumor-assocated antigen (hlTAA) is being evaluated for its potential use in diagnosis and/or monitoring of lung cancer patients. The antigen detected is immunochemically cross-reactive with a normal plasma protein, alpha 1-antichymotrypsin (ACT). Studies have been aimed at eliminating or circumventing interference caused by ACT in the RIA. We have demonstrated that the two proteins differ in their binding site for chymotrypsin since a) ACT totally inactivates the enzyme whereas the hlTAA has no effect on chymotrypsin activity, and b) only ACT will bind to insolubilized chymotrypsin/agarose. Initial attempts to remove all cross-reactive ACT from plasma using chymotrypsin/agarose have so far been unseccessful, but these studies will continue. The RIA in its present form has been used to examine sera from more that 130 normal individuals as well as from over 300 lung cancer patients. In addition 24 lung cancer patients have been sampled serially for periods of 5 to 19 months. In general there is positive correlation between marker level and disease status. A murine T cell hybridoma was prepared which, after cloning, is a stable producer of macrophage migration inhibitory factor and macrophage activating factor. It will be used as a source for future purification and characterization of these lymphokines.