AbstractMarlin‐1 is a GABAB receptor and Jak tyrosine kinase‐binding protein that also associates with RNA and microtubules. In humans and rodents, expression of Marlin‐1 is predominantly restricted to the brain, but expression in lymphoid cells has also been reported. Here, we have studied the distribution of Marlin‐1 in testis and spermatozoa. Our results indicate that Marlin‐1 is highly expressed in testis. The protein is abundant in spermatogonia, spermatocytes, spermatozoa, and Sertoli cells. We also have studied the subcellular distribution in spermatozoa. Marlin‐1 is present in the tail and to a lesser degree in the head of the sperm cell. Finally, we have explored two protein interactions. Our findings demonstrate that Marlin‐1 associates with a microtubule fraction and with GABAB receptors in testis suggesting that the set of protein interactions of Marlin‐1 are conserved in different tissues. J. Cell. Biochem. 103: 886–895, 2008. © 2007 Wiley‐Liss, Inc.