Replication, persistence and expression of the exogenous DNAs (pCH110 and pDOJ-tyr) were investigated after microinjected into the fertilized Xenopus eggs. Southern hybridization results showed that the exogenous gene existed extrachromosomally during early development: it seemed to remain unreplicated until blastula stage and degrade gradually afterwards. Persistence was different depending on the conformation of the injected DNA: the supercoiled form lasted longer than linear and nicked forms. Several different promoters linked to E. coli β-galactosidase gene were microinjected to test correct expression during the early amphibian development. Among these, vectors containing cytoplasmic actin and SV40 early promoter were expressed actively. Although little amount of the injected exogenous lac Z genes persisted after gastrula stage, the activity of β-galactosidase was still detected. Finally, we observed that there was a difference between the time of enzyme production using Western blot and the onset of enzymatic activity by histochemical enzyme assay using X-Gal, which might be due to either the sensitivity of enzyme assay methods or post-translational regulation.