By simultaneously measuring amino acid incorporation and respiration, it is estimated that in germinating barley seeds, only 1% of the energy released from inspiration is use for protein synthesis. This estimate is based on the assumption that (1) all O2 absorbed by the seeds is used for respiration; combustion of 1 glucose with the aid of 6 O2 yields 36 ATP; (2) protein synthesis involves assembly of preformed amino acids; the main energy expenditure is for making peptide bonds; formation of each peptide link requires 4 ATP; (3) specific radioactivity of the amino acid in the incubation medium reflects that of the precursor pool inside the seeds. The first and the third assumptions could be incorrect, therefore, the actual energy consumption for protein synthesis might be much higher.