The present paper describes the expression of a target fusion gene, WAP/hGH fused to the EGFP-expressing gene in transgenic mice derived from the transfer of transgenic embryos selected because of their expression of enhanced green fluorescent protein (EGFP). The 6.7-kb fusion gene was microinjected as a single cassette gene construct into the pronuclei of mouse zygotes. The surviving embryos were cultured and were classified according to the EGFP expression patterns at the morula or blastocyst stage. After the transfer of embryos with uniform-expression or mosaic-expression of EGFP, transgenesis occurred in 85.7% to 86% or 44.1% to 44% of the pups, respectively. No transgenic pups were derived from EGFP negative embryos. In the transgenic females, EGFP was ubiquitously expressed under the control of the CAG promoter, and hGH was expressed under the control of the WAP promoter in an appropriate fashion: hGH was secreted into the milk of lactating transgenic females. The presence or absence of the expression of EGFP coincided with that of the hGH gene in the transgenic mice. The present cassette gene construct is a useful example for circumventing the routine analyses of DNA and RNA required for the generation and maintenance of transgenic lines.