The synthesis of two modified genes, CryIA(b) and CryIA(c), each consisting of 1845 bp, is described in detail. The genes were synthesized using an improved PCR procedure based on recursive principles. The synthetic CrylA(c) gene was put under the control of a maize ubiquitin promoter. This construct was tested in a maize endosperm-derived suspension culture system. The use of maize endosperm culture as a quick and efficient system to test the activity of synthetic genes is described.