The amounts of mRNAs for 72 kDa (HSP72) and 73 kDa (HSC73) heat shock proteins were measured semiquantitatively with competitive polymerase chain reaction (PCR) techniques after reverse transcription (RT) using a heterologous DNA fragment (PCR mimic) as an internal standard. The changes of signal intensities of PCR products were well correlated with the amount of mRNA in rat brain measured as optical densities of Northern blot. Thus, an analysis with mimic RT-PCR technique provides a rapid, semiquantitative, and safe method to detect changes of HSP72 and HSC73 mRNAs after brain ischemia.