A holographic technique has been used to measure the quantum yield for photochemical product formation from two excited triplet states of biacetyl in a polymer host. The technique involves a simple measurement of the time taken for the hologram to reach its maximum diffraction efficiency. This measured time can be directly related to a photochemical quantum yield. The diffraction efficiency from the lowest triplet state has a yield of 0.045 ± 0.010 measured in this way as compared to a value of 0.03 ± 0.005 determined by a direct absorption method. The triplet state 13 000 cm-1 above the lowest triplet state has a quantum yield of 0.7 ± 0.02 determined by the holographic technique. © 1985 American Chemical Society.