Glycol methacrylate has been used as an embedding medium for studies of spermiogenesis in the salmon. DNA and basic proteins are shown to stain with the same specificity in thick (0.5-1.0 mu) sections of GMA-embedded salmon testes as in sections of comparably fixed, paraffin-embedded testes. Stain can be localized far more precisely in GMA sections than in paraffin sections due to the thinness of the sections and to the excellent structural preservation of nuclei. In addition, ultra-thin sections of GMA-embedded salmon testes can be observed with the electron microscope, and this permits exact correlation between nuclear fine structure and chemical composition in consecutive sections of the same nuclei.