We observed that particularly the expression of UBC and HPRT1 in HT29 and MRPL19 in SW480 was significantly altered by changes in serum availability disqualifying them as reference genes, even though UBC (Andersen et al. 2004) and HPRT1 (Sørby et al. 2010) were recommended as suitable normalizers for RT-qPCR studies on tissue specimens from CRC patients. The gene discussed is HPRT1; the disease is colorectal carcinoma.