Transient expression is the nonstable expression of a transgene whereby the transgene does not integrate into the host’s genomic DNA. Transient expression assays have 20 years of history in plant molecular biology research, being used to answer a variety of questions. The method described here allows the ability to test promoter activity for seed-specific expression by quantifying reporter protein production in immature seed tissues. This method is especially suited to test vector activity for stable expression, test promoter activity, and discern regions of a promoter that is necessary for transcription in seed tissues. The transient expression assay is a tool that has aided a great deal of molecular biology research.