Protein synthesis was studied in relation to in vitro flower bud formation in tissue strips of tobacco. The rate of leucine incorporation increased from the 3rd day on up to the 7th day. Concomittantly an increment in protein content was observed. Protein synthesis was slow in control explants which did not produce buds. From the first day onwards the nature of the polypeptides synthesized in vitro differed from that of the protein already present in the original explants. However, in spite of the progression of development towards bud formation, there are only a few changes in the complement of the proteins being synthesized during this 6-day period.