The persistence, replication and integration of five different forms of MhGH gene microinjected into fertilized eggs of fish were analyzed. For all forms of novel DNA tested, the replication of the introduced sequences began appeared at the late gastrula followed by foreign DNA degradation, Injected circular molecules (FormI, II) were replicated in FormII, not FormI, without obviously increased copy numbers through blastrulation (3-4 folds). In contrast, extensive and efficient amplification of input linear DNA sequences were seen whenever the microinjected DNA was assembled into high molecular weight, head-to-tail or tail-to-tail concatemers. And the overall copy numbers significantly increased, sometimes reached more than 100 folds from the late blastrula to early neurula stages, in comparison with the copy number injected into the eggs. It must be pointed out that the fate of novel DNAs differed from batches of embryos, different individual, and the input template sizes. Although the majority of linear DNA injected was assembled into long concatemer, FormI and/or FormII DNA were slightly formed, and monomeric was remained in the host eggs. However, these 'free' DNA forms persisted during the early embyrogenetic stages without obvious replication. In addition, the input long linear concatemer was not assembled into any other forms except ligated into higher molecular weight DNA. Using the restriction enzyme digestion and Southern blotting we also analyzed aspects such as the pathways generating concatemers, the timing and the patterns of integration, and the modification or changes of some restriction endonuclease sites along the novel DNA.