Rate constants for the dissociation of highly vibrationally excited ketene (CH2CO) have been measured at the threshold for the production of CH2(B-3(1)) and CO(1-SIGMA+). The rate constant increases in a stepwise manner with increasing energy, consistent with the long-standing premise that the rate of a unimolecular reaction is controlled by flux through quantized transition-state thresholds. The data give the energies of the torsional and C-C-O bending vibrations of the transition state.