We report here the development of convenient dicistronic transgenic markers for the rapid and efficient simultaneous analysis of transgene activity in transgenic mice. Two sensitive histological markers, the beta-galactosidase (beta-gal)-encoding lacZ gene and the human placental alkaline phosphatase (hpAP) gene, have been fused to the internal ribosome entry sequence (IRES) from the encephalomyocarditis virus, which directs efficient mRNA cap-independent entry of the translation apparatus in mammalian cells. The IRES permits efficient translation of either lacZ or hpAP when placed anywhere within transgene exonic sequences, including both 5' and 3' untranslated regions. In addition, the production of constructs for transgenic analysis of DNA regulatory elements is greatly facilitated with IRES-lacZ or IRES-hpAP, since the IRES relieves the need for complicated in frame transgene protein fusions to produce a functional beta-gal or hpAP protein.