Variations in JNK activity between different leukemia samples is not explained by the absolute level of cellular enzyme expression. Lysates from leukemic samples registering negative (nos. 2099, 2127, 2137) or positive (no. 2135) in the solid-phase JNK assay were immunoprecipitated and immunoblotted to show the presence of JNK protein in the lysates. Half of each immunoprecipitate was placed in an immune complex kinase JNK assay. Note the inactivity of immunoprecipitated JNK1 within no. 2099, despite the presence of a similar protein amount as no. 2127. Also note the apparent absence of immunoprecipitable JNK in the HL-60 cell line.