Chemokine-like factor (CKLF) was isolated from PHA-stimulated U937 cells. It is composed of 152 amino acids and located on chromosome 16q22. Utilizing bioinformatics, based on CKLF cDNA and protein sequences, in combination with experimental validation, we identified a novel gene designated chemokine-like factor super family member 1 (CKLFSF1). CKLFSF1 maps on chromosome 16q22, and the full-length gene comprises of seven exons and six introns. Using RACE-PCR, we identified two potential alternative transcription start sites, 1A and 1B. Northern blot and RT-PCR analysis demonstrated that CKLFSF1 is predominantly expressed in human testis tissue, with only lower levels of expression in many other human tissues. RT-PCR and cDNA sequencing identified 23 alternatively spliced isoforms of CKLFSF1 in the testis tissue, which encode protein variants ranging from 36 to 169 amino acids in length. Immunohistochemistry analysis demonstrated that CKLFSF1 proteins are highly expressed in spermatocyte and in tissue fluid of human testes tissue. In light of these findings, we propose that CKLFSF1 may play an important role in spermatogenesis or testicular development. © 2004 Elsevier Ltd. All rights reserved.