Northern analysis of the mouse testis and liver RNA show two types of lanosterol 14alpha-demethylase (CYP51) transcripts, somatic and a testis-specific transcript. At least two CYP51 mRNAs are expressed in liver and testis, while the smallest transcript is expressed only in testis. The partial mouse Cyp51 cDNA (1052 bp) was obtained by RT-PCR cloning and was also found in expressed sequence tag (EST) clones. Bacterial artificial chromosome (BAC) clones containing mouse Cyp51 gene were also found. The coding part of the partial mouse CYP51 is 93.9% homologous to the rat and 87.9% to the human CYP51 cDNAs. There is less than 2% variation between the CYP51 EST clones to the RT-PCR cloned partial cDNA and BAC clones.