Since previous studies have suggested that the mammalian protamine mRNAs are translated poorly in cell-free systems, we directly measured the efficiency of translation of mouse protamine 1 mRNA. We found that mouse testis poly(A)+ mRNA stimulates the synthesis in the wheat germ and reticulocyte cell-free systems of three prominant translation products which can be resolved by electrophoresis through acid urea polyacrylamide gels containing 8 M urea. These translation products have been identified as testis-specific protein, protamine 1, and the precursor to protamine 2 by several criteria, including labeling with amino acids, [35S]cysteine, and [3H]leucine, which are known to be specific to some of these proteins from the nucleotide sequences of recombinant DNAs. Surprisingly, the mobility of the testis-specific protein translation product is slightly reduced and the mobility of both protamine translation products is drastically reduced unless the extracts of cell-free translations are coelectrophoresed with the appropriate carrier. The fraction of [35S]cysteine- labeled protamine 1 translation product was compared with the fraction of testis poly(A)+ mRNA as protamine 1 mRNA which we measured in dot blots with the use of an SP6 RNA polymerase transcript for protamine 1. The results demonstrate that protamine 1 mRNA is translated only slightly less efficiently than the average testis poly(A)+ mRNA.