Classical Northern blot analysis for measuring mRNA requires too many cells to be practical for cell sorting. Yet, measurement of gene expression in small subsets within a heterogeneous population of cells is often desired. The PCR in combination with prior reverse transcription (RT-PCR) of the mRNA of interest provides a means for measuring gene expression using as few as one cell. When RT-PCR is performed, the reliability of the data can be highly subjective due to the efficiency of both RT and PCR steps. This subjectivity can be eliminated by a technique for quantitating specific RNA molecules using an internal RNA competitive reference standard (RNA-CRS), which is identical to the sequence of interest except for a deletion of 80 bases. Here we illustrate a strategy for quantitative PCR using a RNA-CRS, synthesized solely using nonplasmid-based PCR techniques. The competitive reaction consists of a constant quantity of wild-type mRNA (from 100-1000 cells) added individually to tubes containing a serially decreasing amount of RNA-CRS. The RT-PCR is performed on these samples, then the resulting product is analyzed by gel electrophoresis and densitometry. The procedure for preparing the RNA-CRS and subsequent RT-PCR steps are described in detail.