Alphavirus vectors have become an important complement to the systems
available for transient expression of cloned sequences in cell culture
and in vivo. They express foreign sequences from cytoplasmically self
-replicating RNA, which can be delivered into the cell either as RNA o
r DNA. This article outlines some of the properties of alphavirus expr
ession systems, and discusses the pros and cons underlying their prese
nt use in basic research and for in vivo applications.