Numerous human cancers are accompanied with the increase of ferritin content in blood serum. Ferritin is composed of light and heavy chains, encoded by FTL and FTH genes, respectively. The analysis of EST database showed that the expression of FTL and FTH genes in lung tumors is decreased compared to normal tissues, and is not altered in renal cancer cells. The alteration of mRNA corresponding to FTL and FTH genes was estimated by real-time PCR in primary lung and kidney tumors. A significant and frequent inhibition of FTL and FTH gene expression (on average by 11 and 9 times, in 83% (33/40) and 73% (11/15) of cases, respectively) was detected in primary squamous lung carcinoma. The expression of these genes was not altered so significantly (by 6 and 3 times, in 58% and 27% of samples) in clear cell renal cell carcinoma. Our work reports for the first time the down-regulation of FTL gene expression at the first stage of lung cancer (10/10), and proposes this gene as a potential oncomarker for early diagnosis. The FTL mRNA content may be quantified by non-competitive hybridization on expression DNA microarrays. The possible causes of a serum ferritin increase in lung squamous cell carcinoma and clear cell renal cell carcinoma are discussed. © 2009 Pleiades Publishing, Ltd.