Tryptic [32P]phosphopeptides were prepared from [32P]phosphorylated ox‐kidney branched‐chain complex and analysed by high‐voltage paper electrophoresis at pH 1.9. In the maximally phosphorylated complex 3 tryptic [32P]phosphopeptides were identified (TA, TB, TC). RF‐values relative to N6‐dinitrophenyllysine were (mean ± SEM for 25 obs.): TA, 1.53 ± 0.03; TB, 1.07 ± 0.02; TC, 0.65 ± 0.01. Relative rates of phosphorylation were TA > TB > TC. Phosphorylation of TA reached a maximum when about 66% of the complex was inactivated. Phosphorylation of TB and TC was associated mainly with 66–95% inactivation of the complex.