This short communication discusses the use and limitations of housekeeping genes as internal standards in quantitative studies of RNA expression. Commonly used housekeeping genes include glyceraldehyde-3-phosphate dehydrogenase (G3PDH), albumin, actins, tubulins, cyclophilin, hypoxantine phosphoribosyltransferase (HRPT), L32, 28S, and 18S rRNAs. The authors highlight that these genes can vary in expression under different conditions, as demonstrated through three experimental examples involving nerve cells, immune cells, and cytokine mRNA synthesis. They recommend using 28S and 18S rRNAs as internal standards due to their minimal variation and suggest using at least two types of housekeeping genes to ensure reliability. The paper also provides guidelines for handling RNA samples and interpreting data to minimize experimental variations.This short communication discusses the use and limitations of housekeeping genes as internal standards in quantitative studies of RNA expression. Commonly used housekeeping genes include glyceraldehyde-3-phosphate dehydrogenase (G3PDH), albumin, actins, tubulins, cyclophilin, hypoxantine phosphoribosyltransferase (HRPT), L32, 28S, and 18S rRNAs. The authors highlight that these genes can vary in expression under different conditions, as demonstrated through three experimental examples involving nerve cells, immune cells, and cytokine mRNA synthesis. They recommend using 28S and 18S rRNAs as internal standards due to their minimal variation and suggest using at least two types of housekeeping genes to ensure reliability. The paper also provides guidelines for handling RNA samples and interpreting data to minimize experimental variations.