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The myristoylated protein-tyrosine kinase, p56lck, is expressed predominantly in T cells where it is believed to play a role in T cell activation. We observed a 56-kDa protein that became metabolically labeled in intact T lymphoid cells that were incubated with either [3H]myristate or [3H]palmitate. This protein was identified as p56lck based on its specific immunoprecipitation with polyclonal antisera to p56lck, by induction of a shift in its electrophoretic mobility following treatment of cells with 12-O-tetradecanoylphorbol-13-acetate and by co-chromatography with p56lck on protamine-agarose. Characterization of the two acylation events revealed that, in contrast to the p56lck-associated radioactivity from [3H]myristate-labeled cells, the p56lck-associated radioactivity from [3H]palmitate-labeled cells was susceptible to cleavage by neutral hydroxylamine and was not blocked by inhibitors of protein synthesis. Pulse-chase …