In Xenopus oocytes, the level of spermine is as high as spermidine, but it decreases during oocyte maturation, and becomes very low in early embryos. The level of putrescine is 3-4 nmoles/embryo, spermidine is ca. 1 nmole/embryo, and that of spermine is ca. 0.02 nmoles/embryo throughout early embryogenesis. To obtain clues to understand the developmental significance of the unique polyamine composition, especially that of the very low level of spermine, we performed experiments to overexpress S-adenosylmethionine decarboxylase (SAMDC) that provides aminopropyl group to form spermidine from putrescine and spermine from spermidine, respectively. The expression of SAMDC of ca. 400-folds over its endogenous level resulted in a considerable decrease in the level of putrescine with a concomitant increase in the level of spermidine, but the level of spermine did not change at all. The SAMDC over expression, however, induced exhaustion of S-adenosylmethionine (SAM), which was followed by the execution of apoptosis at midblastula transition (MBT). We then performed experiments to directly inject spermine into Xenopus early embryos together with or without in vitro-synthesized mRNAs (β−catenin mRNA and GFP mRNA). It turned out here that spermine (2 nmoles) injected at ca. 100-folds over its endogenous level, the level comparable to that of the endogenous spermidine, strongly suppressed development. However, spermine (0.4 nmoles) expressed ca. 20-folds over its endogenous level, did not interfere with development, yet almost completely inactivated co-injected mRNAs probably by direct binding. Spermine (0.16 nmoles/egg) expressed ca. 8-folds over its endogenous level, inhibited neither development nor mRNA translation. Thus, it appears that, unlike putrescine and spermidine, spermine has to be maintained at low levels (0.02-0.2 nmoles/embryo) for normal development in Xenopus embryos.