Fluorescent in situ hybridization was combined with flow cytometry to detect the expression of the double-stranded-RNA-induced protein kinase (PKR) in single cells. Labeled anti-sense oligonucleotide was used to target the specific mRNA while the protein was targeted with an antibody. It was demonstrated that the PKR-mRNA signal could be protected through a lengthy immunostaining procedure. The expression pattern of the PKR-mRNA with respect to DNA content was shown to be comparable to that of 18S ribosomal RNA.