We have cloned and sequenced a protamine gene from the chum salmon (Oncorhynchus keta). This gene sequence is highly homologous to one found in the rainbow trout (Salmo gairdneri), including the conservation of two structurally different repetitive elements. One of these repeats resembles a nonviral retroposon and the second is similar to a retroviral-like transposable element. The degree of sequence divergence between the O. keta and S. gairdneri genes is much less within the transcription unit than in the repetitive elements or the remainder of the flanking DNA, suggesting that since the coding and the untranslated regions are highly conserved, both contribute significantly to the structure and stability of protamine mRNA (or its cognate messenger ribonucleoprotein) and this may be important for the translational control of protamine synthesis.