Identification of genes that are specifically expressed in the adult testis or the fetal testis is important for the study of genes related to the development of the testis. In this study, a human testis cDNA microarray was established. PCR products of 9216 clones from a human testis cDNA library were dotted on a nylon membrane; mRNA from adult and fetal testes were purified and probes were prepared by a reverse transcription reaction with testis mRNA as template. The microarray was hybridized with probes of adult and fetal testes, and 96.8 and 95.4% of clones were positive, respectively. In total, 731 clones were differentially expressed: 592 were highly expressed in adult testis and 139 were highly expressed in fetal testis. Among these genes, a new reticulon (Rtn)-like gene was detected and named Rtn-T. Rtn-T was highly expressed in adult human testis. The cDNA of Rtn-T contains 3491 bp and the putative protein had 968 amino acids. This protein is homologous to the six known members of the Rtn family (KIAA0886, Rtn xL, reticulon 4a, Nogo-A, Nogo-A short form, and brain my043) but was different at the 5' end. All homologues originate from one gene, and result from both different promotor regions and different splicing. Rtn-T lacks the first exon and contains a second exon that is lacking in the other homologues. Rtn-T is shorter than KIAA0886, Rtn xL, reticulon 4a and Nogo-A, but longer than the Nogo-A short form and brain my043. Sequence analysis showed that Rtn-T protein has two hydrophobic regions that may be membrane-spanning domains. Expression profiles showed that Rtn-T is specifically and strongly expressed in testis. The results of the present study indicate that the Rtn-T gene is differentially expressed in adult and fetal testes and encodes a membrane protein that may have a function in testis development.