The mouse t-complex is known to harbour genes which affect male fertility. Tcp-11 is a t-complex gene which is only expressed in male germ cells and from its position is a candidate for a distorter, one of the two types of genetic element involved in transmission ratio distortion. Antibodies raised to TCP-11 protein made in E. Coli were used on thin sections of testis and shown to recognise late spermatids. On Western blots the antibodies bound to a 68-kD protein present in protein extracts from testis. No specific signal could be detected using the antibody on protein extracts from other mouse tissues. Following gentle lysis of the germ cells and fractionation on sucrose gradients, all the material recognised by the anti-Tcp-11 antibody was found to be soluble and unassociated with any membrane fraction or organelle. A comparison of the time course of expression of the Tcp-11 mRNA and the TCP-11 protein revealed that expression of this gene is under translational control.